For me it's mostly reason one and three - I can literally count on one hand the times in my life (and I don't even need all the digits) where I have been sexually attracted to anyone (for me it's men, as I am hetero-romantic). Considering that I'm going to be 43 very soon, that seems like an un-naturally low number of people to be attracted to (this of course means real people, not celebrities and fantasy characters) so hence the grey-A label. Outside of those instances, I have had plenty of instances where my libido rears its head, but other than taking care of it myself I have no desire to find a partner to help me squelch it, hence #3.
The very first real sexual attraction (to a real person) I ever experienced was when I was 14 (and I use the term "sexual" very loosely here - will explain later), and at that time I was simply too young (and the object of my infatuation too old) for anything to develop.
From then on I would have minor "squishes" on various celebrities (I swear I had a crush on half the Baltimore Orioles baseball team when I was 13! ) - in other words, people I would never have a chance with. As I got older, into my late teens and early 20's, I began to wonder if something wasn't wrong with me because whenever I'd have a crush I could never imagine wanting to have sex with the guy (let's say even if by some chance I had a chance with a famous person). I would fantasize and masturbate away but could never even begin to think about a guy putting his penis into my vagina (and oral sex was just gross, gross, gross!). Actually if that thought crossed my mind during a fantasy, that was a surefire way to kill it! Kinda like a mental cold shower.
As I got into my early 20's I got into therapy for unrelated reasons and eventually I got around to asking my therapist about this issue. She really had no idea why I might be sex averse, but she told me that I could train my mind to want to have sex with someone I was attracted to. So I did try her suggestion, and really had little luck with it (I suppose it was like trying to acquire a taste for a food you have no desire to eat). The only reason I ever wanted to try to want sex was that I was hoping I could have a relationship and naturally figured that the vast majority of men would want sex at some point. Otherwise, I figured there would be no point in me persuing relationships if I could never get aroused by the idea of having sexual intercourse.
So when I was 24 I met this man one day at work (he didn't really work there, he was just there to do some contracting work) and I developed a serious crush on him. But still there was the problem of sex - basically I was just romantically attracted to him and never thought about or desired sex with him. However, somewhere along the way I continued to follow that therapist's advice and eventually somehow taught my mind to want to have sex with him, even though some part of me still never wanted to actually follow thru. He was receptive to the idea of having sex with me, but eventually I turned him down (one big reason was that it would only be sex, since I found out later that he had a live-in girlfriend, and there were tons of other smaller red flags). So had circumstances been different, I probably could have had a sexual relationship with this man and possibly even wanted and enjoyed sex.
Then I went several more years (between these episodes there was nothing - no attractions, no crushes, nothing) and again met a man at work (he actually worked for the company and was there everyday like I was) who I fell for. Well, at this point I finally had gotten to better "acquire the taste" (I had never actually had sex, just what I could imagine in my mind) and did indeed many times imagine dragging this guy into the closet under the stairs and pouncing on him for some sexual action. But I never got the chance to cross that final bridge of choosing whether or not to have sex with him as I did with the last guy. This guy was eternally wishy-washy and kept breaking up (that's when I'd make a move) with his GF but he kept going back to her and breaking up in an endless cycle, and it became so very depressing to wait around for some wishy-washy guy to make up his mind once and for all. So then began another drought of nothingness. But this one was, unlike the others, short-lived, and when I was around 30 I met another guy with whom I had had a professional relationship and I fell for him. Didn't work with him, just a professional dealing where I had hired him to do some work for me (and I did a little work for him in a trade of sorts). Again, I was able to imagine having sex with him, and indeed this was by far the most powerful sexual attraction I've ever felt so far in my life. It was all I could do (sorry this sounds like some kind of bad romance novel) to restrain my self from pouncing on him when I was with him in his office. I had been flirting with him and he with me (probably the only time in my life when I was able to figure out what flirting was and how to do it, somehow it just came naturally at that point but probably only because I was in the throes of a heavy-duty attraction) but that's about as far as it ever got. Eventually he told me that he was moving his business back to his home state (which was far from where we currently were) and at that point I no longer had any business dealings with him. I wanted to escalate things into some kind of a formal relationship (outside of business and just flirting and chit-chat) but it was at this point he revealed to me that he was bi-sexual (just assuming the bi part, as generally gay men don't flirt with straight women in a serious way) and had a male partner who he was going home to meet. Needless to say I was devastated, especially since this was the closest thing I've ever had to developing into a serious relationship in my whole life. That and the fact that he led me on for so long and made me think I had a chance and then came out to me in that way. Well, he moved back home and I never saw him again, and after that I had some other rotten things happen in my life and not long after that I ended up also moving back home, back in with my parents out of necessity.
That was 13 years ago, and since then I've had no more attractions (romantic or sexual or both) to anyone since. I still have a libido (which is mostly iced now due to me being on the pill) and masturbate once in a blue moon, and while I may imagine sexual intercourse once in a while, I think of no one in particular.
So, compared to a typical female sexual, I am of course not totally A since I have had a few sexual attractions, but I think that my level of attractions falls far short of what is "normal" (hate that word, I prefer the term "default" - in that is the typical situation) in a sexual woman. Even if I had managed to have been able to have an actual relationship with any of the three men, and had engaged in intercourse, I still would be a grey-A since these desires are so very rare in me and I never seek them out (all these incidences were accidental crushes - I didn't date or try to meet them on the basis of establishing a romantic or sexual relationship). That, and the whole thing of having to train my self to imagine wanting sex - in other words it did not come naturally for me like it apparently does for most women.