TPO (TOEFL Practice Online) 是美国教育考试服务中心(Educational Testing Service，简称ETS)专为参加
1. 阅读要点概括：
Main point: Scientists have advanced several hypotheses to explain this decline.
Sub point 1: The yellow cedar decline may be caused by insect parasites, specifically the cedar bark beetle.
Sub point 2: A second hypothesis attributes the decline to brown bears.
Sub point 3: Gradual changes of climate may be to blame.
2. 听力要点概括：
Main point: We still do not know what is killing the yellow cedar. None of the explanations discussed in the reading is adequate.
Sub point 1: These healthy yellow cedars are generally much more resistant to insect infection than other tree species.
Sub point 2: Bears cannot be the reason for the decline, because islands cedars are decreasing without bears.
Sub point 3: Although the climate change may have made the cedar roots more sensitive than they used to be, this is not what killed them.
TPO逐题精讲”能有效帮助您查漏补缺，完美备考。
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