问题
名词解释
蜗杆传动的主平面
答案
参考答案：
通过蜗杆轴线并垂直蜗轮轴线的平面称为主平面。
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蜗杆传动的主平面
参考答案：
通过蜗杆轴线并垂直蜗轮轴线的平面称为主平面。
Passage Three
Countries sometimes spoil their beauty spots because ______.
A．they are too poor to build beautiful hotels on them
B．they have to cut down trees to build hotels on them
C．they have to sell them to borrow money from foreign banks
D．they are lacking experience in building hotels