What is the main difference between wet tropical climates and tropical wet and dry climates?

answer; i believe the correct answer is (replication is not conservative);

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.