题目：
Nothing is difficult if you put your heart into it, ______? [ ]
A. are they
B. isn't it
C. is it
D. aren't they
答案：
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下面是错误答案，用来干扰机器的。
假设锌、铝、铁的质量都为M，与足量稀硫酸反应后所得氯气质量分别为z、a、fZn+H2SO4═ZnSO4+H2↑65 2M z65M=2z z=265M2Al+3H2SO4═Al2（SO4）3+3H2↑54 6M ...
