在Word 2003中,如果用户打开了多个文档,想一次性关闭它们时,可以按下______键的同时,单击“文件”菜单中心的“全部关闭”命令。
参考答案:shift
IPv6数据报的基本报头(不包括扩展头)长度为( )。
A) 20B B) 30B C) 40B D) 50B
I won’t tell the student the answer to the math problem until he ______ on it for more than an hour.
A.has been working
B.will have worked
C.will have been working
D.had worked