Lucy ______ her homework this morning, but she didn't.
A. may be doing
B. must have done
C. should have done
D. can do
_____
A. 在键盘上单击BackSpace键
B. 右击打开快捷菜单，再选择“删除”命令
C. 在“编辑”菜单中选用“剪切”命令
D. 将该文件属性改为“隐藏”
_____
A. 交
B. 连接
C. 笛卡儿积
D. 自然连接
While ______ the museum, I encountered an old classmate.
A. visit
B. visited
C. be visiting
D. visiting
微信支付 
支付宝支付