It's pretty hard to explain.

　　這事很難解釋清楚。

　　The description was pretty vague.

　　這項描述是相當含糊的。

　　That's a pretty stretch of coast.

　　那是一段美麗的海岸線。

　　You looked pretty upset just now.

　　你剛才看上去很沮喪。

　　She had a pretty tough childhood.

　　她度過了一個非常艱苦的童年。