Yes. I wear boys small crew neck to shirt. They are so comfortable and keeps me feeling clean. then of course helpful if I'm wearing something otherwise revealing in one way or another-- but not limited to.
But I don't wear a bra / under shirt / t shirt. That'd be too many layers id end up tugging on stuff bc I hate bunching.
I answered A but it all depends on the shirt. If I am going to work, I don't want my tits hanging out, but if its a night our with my SO, and I want to look sexy, I may forgo the undershirt and let the girls out for some air ;-)