Which of these characteristics is common only at the embryonic stage of fish and humans, and is suggestive of a common ancestor between the two?

answer; a male inherits only one allele of the x-linked gene controlling hair color;

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.