Directions: Identify the sentence(s) or part(s) of sentence(s) that is/are correct in terms of grammar and usage (including spelling, punctuation and logical consistency). Then, choose the most appropriate option.

A. Generally speaking, the harder a student studies,

B. more marks he is likely to get.

C. Most sand dunes are always in motion as wind pushes sand

D. upward one side of each dune,

E. over the top, and down the other side.