only 修饰介词短语：

Only after a bitter struggle was the aim achieved.  这个目的只有经过艰苦的斗争才能达到。

mainly 修饰介词短语：

The rise in price is mainly due to economic factors. 价格的增长主要是经济因素造成的。

just 修饰从句：

Just when she had reached the most important point we were cut off. 她刚刚讲到最要紧的地方，我们的电话就被切断了。

perhaps 修饰从句：

Perhaps because he lived above so many stairs, no one bothered to visit him. 或许因为他住得这么高,没有人愿意爬那么多层楼梯去看他。