since 时间的时态,什么时候用现在完成时,什么时候用现在完成进行时

问题描述:

since 时间的时态,什么时候用现在完成时,什么时候用现在完成进行时
she_______in the elementary school since she graduated from college in 1990.
a/ taught b/ has been teaching c/ was teaching d/ has taught

选择B吧.现在完成时和现在完成进行时的区别:前者强调动作从过去持续到现在,而后者则不仅强调动作从过去不间断持续到现在,还包含将要继续持续下去的意思.如:It has rained for three days.(雨已经下了3天了); It...