Why did many former slaves migrate to cities?

Which is not a claim kennedy made? a. the fact that communist cuba is so close to american soil is one reason we need to accelerate our space program. b. his decision to shift the study of space to one of the highest american priorities was one of his most important decisions as president. c. within these last months at least 45 satellites have circled the earth. (i think it's this one) d. the mariner spacecraft now on its way to venus is the most intricate instrument in the history of space science. i need this answer really quick, so .