语法总结
if 条件句中的情态动词
The plane could only get over... if it rose... 用 could 表能力，if 从句给出条件。
相似句：
- You can succeed if you work hard.
- We could leave if the weather improved.
关系代词 which
the South Pole which was 300 miles away 中 which 修饰 pole，补充其位置。
相似句：
- This is the town which I visited.
- He found the road which led north.