. Leaves are found on all kinds of trees, but they differ greatly size and shape.A. onB.

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A. on
B. from
C. by
(答案→)D. in
解析：介词的用法。介词in表示“在......方面。句意：“人们发现树上长着各种各样的叶子，但它们的大小、形状大不相同。differ from与…..不同，与本题题意符合。