TOEFL Reading: ETS-TOEFL阅读机经 - 7C5RZU3LY78LSP15L$

According to paragraph 3, what is one reason that looking at leaves may not be very useful when trying to determine the species of a rain-forest tree A. Leaves of rainforest trees often look very different when they are wet than when they are dry. B. Leaves that are exposed to the hot tropical sun dry out and lose their distinguishing characteristics. C. It can be hard to determine whether a leaf has a drip tip or not. D. It can be hard to determine whether a leaf belongs to a tree or to another plant growing on the tree.