1. A certain list consists of several different integers.  Is the product of all the integers in the list positive?

(1) The product of the greatest and smallest of the integers in the list is positive

(2) There is an even number of integers in the list.

I chose A for the answer, but the actual answer was C.  Why B works? can't think it through. please help!

2. In the rectangular coordinate system, are the points (r,s) and (u,v) equidistant from the origin?

(1) r+s=1

(2) u=1-r  and  v=1-s

don't know how to solve this question.   help!

A: 条件(1)单独成立, 回答问题. 条件(2)不成立

B: 条件(2)单独成立, 回答问题. 条件(1)不成立.

C: 条件(1)和(2)合并, 回答问题.

D: 条件(1) 和 条件(2) 各自单独可以回答问题.

E: (1), (2)单独, 合并都不能回答问题.