请教gre大佬一个问题

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One way to predict the effects of global climate change on an ecosystem is to extrapolate current trend in global change factors into the future. A (i)______ of this method is that its predictions (ii)______ actual observation, but the method also makes the questionable assumption that the future will resemble the present.

A. virtue         D. dispense with
B. drawback    E. derive from
C. peculiarity   F. improve upon

答案是AE
我就是很奇怪为什么是a不是c 哪里说这个是优点了

我是最棒的耶耶耶UID??3926573

but前面和后面要分开看：
前半句说：这个方法的一个优点是。。。
后半句说：但是这个方法的假设是值得怀疑的，因为它假设了未来和现在会一样。