Well, the only way you're getting no and no for those last ones is if you're requiring all of the 7 standard biological qualities, instead of most of the 7, as is common.
If you're going for all 7, a zygote isn't alive, as response to stimuli is one of the 7 qualities. And we'd be back to the whole pain response/brain function thing, which isn't the topic at hand.
So:
a) Zygotes, semen, and eggs are all alive, as they reach most of the 7 standard biological qualities for life.
b) Zygotes, semen, and eggs aren't alive, and fetuses are considered alive when they reach all 7 standard biological qualities for life.
c) You're choose to ignore the scientific community's definition of "life" and substitute your own, completely invalidating any discussion of science.