短语讲解：

1. Perfect progressive sentences focus on the completion of an action that is, was or will be in progress.

focus on 致力于; 使聚焦于
例句：The talks will focus on economic development of the region.
会谈将着重讨论该地区的经济发展。

2. Think about this sentence in the past perfect progressive.

think about 考虑…; 捉摸…
例句：I'll have a think about that
我会考虑考虑的。

3. Sometimes we use it to refer to recently completed actions.

refer to 参考; 指的是; 涉及
例句：I mention this point now in passing and shall refer to it again.
这一点现在顺便提一下，以后还会讲到。