掘进机履带跳链的原因()。
A、履带过松
B、张紧油缸损坏
C、驱动链轮轮齿磨损严重
D、截割阻力过大
参考答案:A, B, C
-- Would you like some milk in your tea?
-- Yes, please. But just _________. [ ]
A. little
B. a little
C. a few
腹腔镜胆囊切除术有哪些禁忌证()
A.胆囊无功能
B.高度怀疑胆囊癌
C.伴严重腹腔内感染
D.重度肝硬化门静脉高压症
E.6个月以上妊娠