[求助]请教两道PREP的题目

bao8586

1, is m+z 大于0?

(1) m-3z大于0

(2) 4z-m大于0

这题我选的是E,答案是C,请问是为什么啊.

2, if n and t are positive integers, what is the greatest prime factor of the product nt?

(1) the greatest common factor of n and t is 5

(2) the least common multiple of n and t is 105.

这题答案是B

可是我选的是A.

请大家帮我看看,谢谢了.