钻头使用后期有哪些现象？
参考答案：
（1）扭矩增大且不稳；
（2）钻压，大钩负荷和转盘波动较大；
（3）钻时升高；
（4）钻头成本高。
That day, we______ for the train station when Tom fell and hurt his legs badly.
A．have been leaving
B．were just about to leave
C．have left
D．are just going to leave
_____it was raining hard, ____they decided to start.[ ]
A. Although; but
B. But; although
C. Although; \
D. Though; but
