Make a list of countries/states around the world that insects currently do not reside in.

Iceland, and states like Washington DC. , South Dakota, Connecticut, Idaho, New Hampshire, Delaware, North Dakota, Illinois.

Explanation:

Iceland is one of the only places where people live without insects.

The reason why Iceland does not have mosquitos or other insects is its oceanic climate that keeps them away.

The insects freeze 3 times a year, which makes their survival in Iceland impossible.

The other states are not completely insect-free, however, their number is so small that is considered as like they don't exist.

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.