They sang in the park.They were happy.（合并为一句）They ____ _____ ______ in the park.
问题描述：
They sang in the park.They were happy.（合并为一句）They ____ _____ ______ in the park.
答
They were singing happily (副词修饰形容词happy) in the park.为什么要说singingwere是be动词were的过去式，be动词后面的动词应该用ing形式。