在钻井过程中,要求方钻杆比单根长()米。
A、1~2
B、2~3
C、4~5
D、4.5~5.5
参考答案:B
两个不可修复元件故障率分别为0.6次/年和0.8次/年,由这两个元件串联组成的系统的故障率为()。
The new lecture course differs from the old one, ________ the students aren't required to attend lectures.
A.which that
B.that
C.which
D.in which