For some traits (such as birth weight in mammals), natural selection favors individuals that are average and the extremes are selected against. this is known as

Directional selection.

Explanation:

This type of directional selection is referred to as stabilizing section where the intermediate phenotypes are favored over those of the extreme. It is referred to as stabilizing selection because it maintains the mean phenotype of the population.

the electromagnetic spectrum includes, from longest wavelength to shortest: radio waves, microwaves, infrared, optical, ultraviolet, x-rays, and gamma-rays.

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.