我托福写作考了29分.我大概改了下你的文章,写得不错,三个论点都很清晰地表达出来了.
The author offers several explanations for the decline of yellow cedar.However,
the speaker rejects all of them by providing several counterarguments.
First,the speaker opposes the author's opinion that the decline of the yellow
cedar is caused by insect parasites,especially by cedar bark beetles.Instead,
he explains that cedar bark beetles only attack damaged and sick yellow cedar
because healthy ones contain toxic chemical inside that the beetles try to
avoid.So if the beetles suffer from the chemical in the yellow cedar and
choose to stay away from it,they cannot contribute to the decline of yellow
cedar.
In addition,the author proposes that brown bears may be the cause of the
decline.However,the speaker casts doubt on this hypothesis by explaining that
yellow cedar trees are all over the place,but there is a decline of yellow
cedar in places where brown bears do not exist.Therefore,the decline of yellow
cedar cannot be blamed on brown bears either.
Finally,the speaker suggests that climate change is not the explanation either.
He explains that in contrast to the explanation in the reading that yellow
cedar trees are frozen by the cold climate,yellow cedar trees in the lower
areas where the climate is much warmer are more likely to decline than the treesin higher places.This proves the climate change theory is also not possible.