it is/has been+时间段+since since后面接完成时还是一般过去?求例子详解!拜谢~

it is/has been+时间段+since since后面接完成时还是一般过去?求例子详解!拜谢~
it is/has been+时间段+since since后面接完成时还是一般过去?
求例子详解!拜谢~

it is/has been+时间段+since since后面接完成时还是一般过去?求例子详解!拜谢~
用一般过去时
例如：
It has been a while since the last time I saw you.
有好一阵子没见你了.
It has been a few decades since the computer came into being.
自从计算机问世以来已经有几十年的时间了.
It is years since I enjoyed myself so much.
我多年都没有这么高兴了.
It is five years since the boy was a Young Pioneer.
这个男孩不当少先队员已经五年了.