since引导一个时间状语从句时,时态 since引导一个时间状语从句时,从句何时用一般过去式,何时用现在完成时? 例如:——Have you known Dr.Jackson for a long time? ------Yes,since he jioned the Chinese Society. since后的句子为什么是一般过去式,而不是现在完成时
首先,since表示"自从.以来",表示的动作是从过去以来一直持续到现在,所以since引导的从句要用一般过去时态,但主句只能用现在完成时态,因为现在完成时态表示的动作就是从过去一直持续到现在.如以下句子. I have taught English since 1999. I have lived here since I worked here. He has been here since he joined the army;
1 since的意思是“从....的时候开始”,一般情况下,都是从过去某时或某个动作算起,因此用 since引导的句子都是一般过去时。 2 现在完成时表示“从过去某时开始延续到现在的动作”,和since引导的从句搭配正合适。 常用的句子结构就是 现在完成时+since从句 eg I have been here since I was born....
看例子 1. It has been 3 years since he began to smoke 自从他开始吸烟已经三年了 2. It has been 3 years since he smoked 自从他不吸烟已经三年了 3. It has been 3 years since he has smoked 自从他不吸烟已经三年了 根据例...