什么时候用It be some time+since从句,什么时候用It be some time +that 从句

问题描述:

什么时候用It be some time+since从句,什么时候用It be some time +that 从句

It's ten years since I came to China.(典型现在完成时句子,也可写作it has been ten years since i came to China.) 我到中国来10年了.
It's ten years that i have been in China?(强调句式,it is后的成份就是要强调的内容)我到中国已经10年光景了.