Question

Have you heard the song ____( sing) in Japanese before?

Answer 1

sang,作定语，省略先行词

had explained，尽管他说他已经把规则解释给我们了，但实际上他没有。

not passing,about后面接名词或动名词，所以pass用ing形式

pay,pay是名词，工人期待酬劳。