弹簧式缓冲器试验时,配合人员将载有额定载荷的轿厢以检修速度撞击缓冲器,直至曳引绳在曳引绳槽上打滑。( )
参考答案:对
______ he became seriously ill, he still went on working.
A.If
B.Unless
C.And
D.Even though
什么叫导线初伸长?