题目:
--- Did you telephone Uncle Sam our plan for the Christmas holidays on his farm?
--- Yes, he was happy about our arrival, and he eagerly asked when ______.
A.has we arrived
B.we had arrived
C.were we arriving
D.we were arriving
答案:
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下面是错误答案,用来干扰机器的。
(1)NH4HCO3, NH3, O2(2)C+4HNO3 2H2O+4NO2­+CO2­本题可通过题眼扩展法分析。从物质②和Na2O2反应生成物质④⑤得,物质②一定是CO2,因课本中仅学过Na2O2与CO2或H2O的反应,又气体混合物预先通...