关于不定式的GMAT语法考点解析

动词demolished的主语是名词contractors，同时contractors也是不定式to keep的隐式主语(implied subject)，动词不定式to keep在这里表示demolished的目的，keep的宾语代词it的先行词是building。

Wrong: The building WAS DEMOLISHED to avoid falling down accidentally.

在这个例句中动词was demolished的主语是building，同时building也是不定式to avoid的隐式主语，但是a building自己不能avoid something intentionally。所以上面的例句是无意义的(nonsensical)。

再看下面这个例句：

Right: The building WAS DEMOLISHED to keep it from falling down accidentally.

这个例句的主语是building，同时building也是不定式to keep的隐式主语，但是代词it是不定式to keep的宾语，指代building。由于building是不定式to keep的宾语，所以上面的写法也是正确的，表示的意思是the same unnamed people who demolished the building wanted to keep it from falling down accidentally.