CO2气体保护焊，采用粗焊丝焊接的气体流量应比细焊丝焊接的气体流量大。
参考答案：对
----Martin Murray used to be afraid of ______ alone.
----But now he realizes that his mother is always there for him.
A．is
B．was
C．be
D．being
原发性闭经
