题目内容：

They sang in the park.They were happy.（合并为一句）They ____ _____ ______ in the park.

优质解答

They were singing happily (副词修饰形容词happy) in the park.

追问：

为什么要说singing

追答：

were是be动词were的过去式，be动词后面的动词应该用ing形式。