Sara just found out that her sister conceived about seven days ago. She rushes to find a book on pregnancy so that she can learn more about it. The book says that around the seventh day of pregnancy the cells of the zygote begin to:

differentiate and/or the embryo has doubled its size. Aging results in a gradual decline in female fertility.

Explanation:

Hope this was helpful

b because they naturally adapt to their environment plz mark brainliest

explanation:

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.