堆焊面积大于150mm×150mm时，应采取（）堆焊。
A、分区
B、一面
C、一半
D、从一头
参考答案：A
______of them has been to Australia several times, so they know the Opera House very well.
A．Both
B．All
C．None
D．Each
下列字符串中可以用作C++语言标识符的是( )。
A．_1234
B．foo～～bar
C．virtual
D．34var
