快考试了，请教！ｐｒｅｐ

1 c and d are integer,is c even?

(1) c(d+1)is even

(2) (c+2)(d+4) is even

answer C

2 B bought 2 stocks ,each one sold 96$, if B had a profit of 20% on the sale of one stock, but a loss of 20% on the sale of other stock,then on the sale of both stocks combined B had ..answer a loss of $8

3 -2x >3y,is x negative ?

(1)y>0  (2) 2x+5y-20=0

answer D 第２个是怎么判断的呢？

第一題

選C

(1)cd+c is even

(2)cd+4c+2d+8 is even

(2)-(1)=3C+2d+8為even，可解出C為even