_____
A. 平均响应时间
B. 平均无故障时间(MTBF)
C. 平均修复时间
D. 数据处理速率
_______
A. 向垂直方向
B. 向水平方向
C. 按住Ctrl键向垂直方向
D. 按住Ctrl键向水平方向
Two hundred cars ________ since the beginning of the year.
A. sell
B. are sold
C. have sold
D. have been sold
By the end of next semester, we ______ more than three thousand new words.
A. have learned
B. will learn
C. will have learned
D. have been learning
微信支付 
支付宝支付