问题
单项选择题
Town T has 20,000 residents, 60 percent of whom are female. What percent of the residents were born in Town T ？（）
(1)The number of female residents who were born in Town T is twice the number of male residents who were not born in Town T.
(2)The number of female residents who were not born in Town T is twice the number of male residents who were born in Town T.
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：C
解析：
(1)不充分：设出生于T镇的女性居民的百分比为x，出生于T镇的男性居民的百分比为y，根据(1)可得x=2(40%-y)，但由此式无法得到x+y的值；根据(2)只能得到2y+y=60%，并解得y=20%，但无法求得x；(1)+(2)可以得到x的值，从而可以得到x+y的值，所以(1)+(2)充分。