某工程双代号网络计划如下图所示，其关键线路有（）条。
A．2
B．3
C．4
D．5
参考答案：C
—What a fine day! Shall we go picnicking.
— . But we need to be home before six o’clock for the football match.
A．Have a nice time
B．Pardon me
C．That’s great
D．You are right
焊接0Cr18Ni9的焊条应选用______。
A．A002
B．A102
C．A132
D．A407
