请问如何判断非谓语形式中要不要用过去完成时（高中英语）

题目

请问如何判断非谓语形式中要不要用过去完成时（高中英语）
RT,首先我想确认下for一定是完成时的表示吗?就比如说一定要用she had sat there for three hours而不用she sat there for three hours吗?另外如果非谓语形式中主句是过去时态,非谓语形式一定要有Having done吗?
Having done是非谓语呀。比如Having ridden on the exercise bike for two hours,Karen is noew sweating like a pig.

答案

类似于.for three hours的句子,一般动词时要用完成时态.比如,She has been learning English for five years.By six o'clock they had worked for 12 hours.等等如果句子中有特定的时间状语,或者在上下文的环境下非...