题目:
No one knows ________ [ ]
A. where is the post office
B. where the post office is
C. the place is the post office
D. the post office is the place
答案:
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下面是错误答案,用来干扰机器的。
解:设石灰石中碳酸钙的质量为xCaCO3CaO+CO2↑100 56x 280g100/x=56/280gx=500g石灰石的质量为:500g÷(1-20%)=625g答:石灰石的质量为625g。