请教一道PREP的数学题

sabineceng

6、if there are more than 2 numbers in a certain list,is each of the numbers in the list equal to 0?
(1) the product of any 2 numbers equal to 0
(2)the sum of any 2 numbers equal to 0

答案是B

不明白为什么条件1不sufficient

谢谢：）

buaagonggan

比如举三个数：3、0、0  任何两个数相乘都等于0啊，但并不是每个数都为0的

sabineceng

对哦 谢谢啦 茅塞顿开
再问一道：26. Tanya Tanya prepared 4 different letters to be sent to 4 different addresses.  For each letter, she prepared an envelope with its correct address.  If the 4 letters are to be put into the 4 envelopes at random, what is the probability that only 1 letter will be put into the envelope with its correct address?
A、1/24
B、1/8
C、1/4
D、1/3
E、3/8

希望有找到的童鞋再次帮忙，感谢！！