单选题 Bowls X and Y each contained exactly 2 jelly beans, each of which was either red or black, One of the jelly beans in bowl X was exchanged with one of the jelly beans in bowl Y. After the exchange, were both of the jelly beans in bowl X black?
(1)Before the exchange, bowl X Contained 2 black jelly beans.
(2)After the exchange, bowl Y contained 1 jelly bean of each color.

【正确答案】 E
【答案解析】[解析] (1)不充分,因为Y碗中的果冻豆的颜色未知;(2)同理也推不出交换之后碗X中含有的果冻豆的颜色;(1)+(2)同样无法回答上面的问题,因为交换前Y碗中的果冻豆的颜色未知。