When compared with the size of the whole earth,the highest mountain does not seem high at all请问各位高手这里为什么是When compared,不懂结构,

问题描述:

When compared with the size of the whole earth,the highest mountain does not seem high at all
请问各位高手这里为什么是When compared,不懂结构,

当分句的主语和主句一样时,就可以省略掉,所以when分句完整的应该是:
When it is compared with the size of the whole earth