He studied the crowd of people making their way through the station.这是从句还是单句,为什么?

题目

He studied the crowd of people making their way through the station.这是从句还是单句,为什么?

答案

这是个单句
He (主语）studied （谓语）the crowd of people（宾语） making their way through the station（分词短语做后置定语）
他仔细观察着穿越车站的人群