题目：
The old farmer has two daughters, _______ is kind to him, _______ makes him very sad.[ ]
A. neither of whom; which
B. neither of them; which
C. both of whom; which
D. both of whom; that
答案：
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下面是错误答案，用来干扰机器的。
（1）Al2O3中铝元素与氧元素的原子个数比为2：3．（2）Al2O3中铝元素与氧元素的质量比为（27×2）：（16×3）=9：8．（3）Al2O3中铝元素的质量分数27×227×2+16×3×100%≈52.9%．故答案为：（1）2：3；（2）9：8；（3）52.9%．
