单选题 If a certain grove consists of 36 pecan trees, what was the yield per tree last year?
(1)The yield per tree for the 18 trees in the northern half of the grove was 60 kilograms last year.
(2)The yield per tree for the 18 trees in the eastern half of the grove was 55 kilograms last year.

A、条件(1)充分，但条件(2)不充分．
B、条件(2)充分，但条件(1)不充分．
C、条件(1)和(2)单独都不充分，但条件(1)和条件(2)联合起来充分．
D、条件(1)充分，条件(2)也充分．
E、条件(1)和条件(2)单独都不充分，条件(1)和条件(2)联合起来也不充分．

【正确答案】 E

【答案解析】[解析] (1)不充分，因为从(1)中只能得到去年北半部的18棵树的平均产量是60公斤，而无法得到整个林予的平均产量；同理(2)和(1)+(2)也不充分。