问题
单项选择题
During a 3-year period, the profits of Company X changed by what percent from the second year to the third year ？（）
(1)The increase in profits of Company X from the first year to the second year was the same as the increase from the first year to the third year.
(2)For Company X, the profits for the first year were $13,800 and the profits for the third year were $15,900.
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．
答案
参考答案：A
解析：
因为从第一年到第三年利润的增加等于从第一年到第二年利润的增加加上从第二年到第三年的利润的增加，所以根据(1)可得公司X从第二年到第三年利润的增加为0，所以(1)充分；根据(2)只能求出公司X从第一年到第三年的利润的增加，而求不出第二年到第三年的利润的增加，所以(2)不充分。