Religion only.
How are you supposed to 'change' sexual orientation? I certainly have never been able to do it. It isn't like a light switch where you can just turn it off or on. It does not work that way.
all of them, under certain circumstances. some are substantially more fluid than others, of course.
When you say fluid, isn't that an orientation unto itself? Eg: Bisexuality
not necessarily. anecdotally, i've heard of quite a few trans women who grew more attracted to men and less to women after starting hrt, for example.