来造个英语句子吧现在完成时+since+一般过去式 造几个简单的句子呀

He has studied very hard since he came to our school。自从他来到我们学校,他学习就非常努力。We have been missing them since they left here自从他们离开这里,我们就一直很想念他们。He has written to me frequently since I fell ill。自从我生病以来,他就屡次给我写信。