It's the third time that I_____(explain)the problem to you

问题描述:

It's the third time that I_____(explain)the problem to you

这是固定句型结构中的时态搭配——【某人第几次做某事】
It /That/This 【is 】the...time that sb 【have done sth】
It /That/This【was】the...time that sb 【had done sth】
填【have explained】