TPO1 Timberline Vegetation on Mountains - 英檢

Paragraph 1：The transition from forest to treeless tundra on a mountain
slope is often a dramatic one. Within a vertical distance of just a few tens
of meters, trees disappear as a life-form and are replaced by low shrubs,
herbs, and grasses. This rapid zone of transition is called the upper
timberline or tree line. In many semiarid areas there is also a lower
timberline where the forest passes into steppe or desert at its lower edge,
usually because of a lack of moisture.

3. Which of the following can be inferred from paragraph 1 about both the
upper and lower timberlines?
1 Both are treeless zones
2 Both mark forest boundaries.
3 Both are surrounded by desert areas.
4 Both suffer from a lack of moisture.


請問一下，答案是2
但是我實在不懂為什麼1不行，應該是我沒有讀懂，
在選答案的時候，就是覺得1和2都對，
麻煩高手解答一下
感謝感謝。

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