核心问题
Various types of reactor have been designed and constructed for a number of different purposes. (STE)
句中的 various types of reactor 的用法是否正确？
词典解答
various types of reactor 和 various types of reactors 的说法都是正确的,请看下面的例证(参见 these sort of):
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So certain types of plant grow all over the stones and their roots go down into the holes between the stones. 因此，石头上面全都长满了某些种类的植物，它们的根都长到石头缝隙中去了。
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Scientists continue to develop new types of plants which produce heavier crops. 科学家们继续培育新型的高产农作物。