问题
单项选择题
Last week a production worker had gross earnings of $390.00. If she worked more than 40 hours last week and was paid 1.5 times her regular hourly rate for each hour worked in excess of 40 hours, how many hours did she work last week ？（）
(1)If she had worked 4 more hours last week, her gross earnings would have been $435.00.
(2)Her regular hourly rate last week was $7.50.
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：D
解析：
本题的正确答案为(D)。由(1)可得，她多工作4小时时，平均每小时的工资为(435-390)÷4=11.25美元/小时，则她正常工资是11.25÷1.5=7.5美元/小时。设她上周工作了x小时，根据题意可得(x-40)×11.25=390-300→x=48小时，所以(1)是充分的；根据(2)可得她一周工作的时间x为：(40×7.5)+(x-40)×7.5×1.5=390→x=48小时，所以(2)也是充分的。