ing形式是表主动，可转换成一个主动句。还能表示进行，如；
Do you know the man standing at the gate?
=Do you know the man who is standing at the gate?
the smiling face=the face that smiles
the boiling water=the water that is boiling.
ed形式表被动，可转换成一个被动句。还能表示完成 如：
Most of the people invited to the party.=Most of the people who/that were invited to the party.
the heated air=the air that is heated
the fallen leaves =the leaves that have fallen.