时态上用现在完成时、一般过去时、过去完成进行时(依据语境及时间状语的要求)语态上可分为主动语态与被动语态。结合这两个因素,可以选择以下四种句型:somebody has done something. somebody did something.somebody was doing something.something has been done by somebody.something was done by somebody.something was being done by somebody.