The female sex cells of a flowering plant are contained in its a) pistil b) pollen c) zygotes d) seeds

I believe it's D, if you research the definition of zygotes it kind of explains that it's the sex cells. But it might also be A, which is part of the female area (ovary/ovule) of the flower.

The answer would be A, a female flowers sex cells are contained in its pistil, the pollen would pollinate the flower by entering the pistil by wind, bees, birds, or brushing against a male flower.