不懂，求几道题的解释

小小照妖镜

What is the value of (x - y)⁴?

(1)The product of x and y is 7.

(2)x and y are integers.


为什么答案是C,而不是E啊？
求大牛解释！


A certain university will select 1 of 7 candidates eligible to fill a position in the mathematics department and 2 of 10 candidates eligible to fill 2 identical positions in the computer science department.If none of the candidates is eligible for a position in both departments, how many different sets of 3 candidates are there to fill the 3 positions?



A.42

B.70

C.140

D.165

E.315     答案是E，怎么算出来的呢？

沙龙

第一题，乘积为7的整数，只有1和7吧

第二题，简单的组合问题啊，7挑1，10挑2，然后乘法原理，