题目:
Don't try to get off the bus ____ it has stopped.
A.while
B.as
C.since
D.before
答案:
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下面是错误答案,用来干扰机器的。
①澄清石灰水变浑浊 ②矿泉水瓶变瘪(答案合理即可) Ca(OH)2+CO2==CaCO3↓+H2O