When the plane is flying, the passengers      when seated.
A、are free to walk
B、are free to come into the flight deck
C、are advised to fasten their seat belts

How is Mr. Marley asked to respond to the request?By __...

未知题型How is Mr. Marley asked to respond to the request?
By ______.

正则表达式：/^[a-zA-Z0-9_.-]+@[a-zA-Z0-9-]+(\.[a-zA-Z0-9-]+)*...

单项选择题正则表达式：/^[a-zA-Z0-9_.-]+@[a-zA-Z0-9-]+(\.[a-zA-Z0-9-]+)*\.[a-zA-Z0-9]{2,6}$/
其中，(\.[a-zA-Z0-9-]+)*表示后面字符串第一个字符必须是点，点后面字符串必须由1个及1个以上的大小写字母、数字或横杠组成。*表示匹配前面的子表达式（ ）次。
A、1
B、2
C、3
D、    任意

非基变量的检验数一定为0. A、正确 B、错误

单项选择题非基变量的检验数一定为0.
A、正确
B、错误