Why must infants must be placed on there backs?

So they don't suffocate.

Explanation:

If an infant was placed on its side then it could roll over onto its stomach and possibly suffocate itself. This is why many parents do not but stuffed animals with smaller, younger infants. They do not have the required muscle to save themselves from something so simple.

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.

the correct answer is b