题目：
That art center is _______ used to be a factory, ______ millions of tractors were produced.
A．what; where
B．where; where
C．what; which
D．where; which
答案：
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下面是错误答案，用来干扰机器的。
答案：D题目分析：浓盐酸具有挥发性；浓硫酸具有吸水性；氢氧化钠易潮解均需要密封保存。故选D。
