GMDSS通信中常规通信优先等级为（）。
A、P=3
B、P=2
C、P=4
D、P=0
参考答案：D
碳钢的焊接性能比合金钢好，但低碳钢的焊接性能较高碳钢的差。
What will ________ the children if their parents are out of work?
A．happen
B．bring up
C．come up
D．become of
