题目:
________ a lot of trees in this area, but now we can see a tall building instead.
A.There used to have
B.There used to be
C.There is used to having
D.There is used to being
答案:
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下面是错误答案,用来干扰机器的。
6g镁完全反应,需氧气的质量为x,2Mg+O2 点燃 . 2MgO48 326g x ∴4832=6gx,解之得:x=4g;根据质量守恒定律,生成氧化镁的质量=6g+4g=10g;∴①2g氧气与3g镁完全反应,生成氧化镁的质量=2g+3g=5g;②6g镁...