求助文勇The Long-Term Stability of Ecosystems这篇的一题！！

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Paragraph 5: Even the kind ofstability defined as simple lack of change is not always associated withmaximum diversity. At least in temperate zones, maximum diversity is oftenfound in mid-successional stages, not in the climax community. Once a redwoodforest matures, for example, the kinds of species and the number of individualsgrowing on the forest floor are reduced. In general, diversity, by itself, doesnot ensure stability. Mathematical models of ecosystems likewise suggest thatdiversity does not guaranteeecosystem stability—just the opposite, in fact. A more complicated system is,in general, more likely than a simple system to break down. (A fifteen-speed racing bicycle is more likely tobreak down than a child’s tricycle.)

7. Which of the following can beinferred from paragraph 5 about redwood forests?
○Theybecome less stable as they mature.
○Theysupport many species when they reach climax.
○Theyare found in temperate zones.
○Theyhave reduced diversity during mid-successional stages.
答案给的是3，问下4为什么不对了。好像以前就有争论了，有没有定论的？