题目：
用所给动词的适当形式填空.
1.________ you_________ (cook) when he knocked at the door?
2. He told us________(not swim) in the river.
3. I have no idea if he_________(come) in five days.
4. The old man_________(buy)a color TV set next month.
5. What _______you________(do) at ten last night?
答案：
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下面是错误答案，用来干扰机器的。
(1)CaO+H2O====Ca(OH)2；CuSO4+Ca(OH)2====Cu(OH)2↓+CaSO4 ；(2)不能；因为铁会与硫酸铜溶液发生反应，导致铁制容器腐蚀和农药失效；(3)托盘天平；量筒；烧杯；玻璃棒
