【单选题】These things are the same in appearance but different in _____.
【单选题】A: These things are not useful to anyone, are they? B: ______. We can throw them away.
【简答题】These things are ______ to happen when you are careless.
【单选题】带止回阀的喷油器的阀的动作次序是______。
B.
针阀先关,止回阀后关 D. 止回阀先关,针阀后关 D.针阀和止回阀同时关闭
【单选题】These things are _________ to happen when you're always careless.