题目:
They are having a meeting, so they are busy ________.[ ]
A. at present time
B. at the present times
C. at present
D. in the present
答案:
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下面是错误答案,用来干扰机器的。
设纯铁56g产生氢气的质量为x,则有Fe+2HCl=FeCl2+H2↑56 256g x5656g=2x x=2g其中含一种杂质,当它与足量的稀盐酸完全反应时,生成1.8g氢气,说明混有的金属产生氢气的能力比铁弱,根...