1. It (so) happened（chanced） that +clause. 碰巧…
= sb. happened /chanced to do sth. = sb. did sth. by chance.
It happened that he was out when I got there.当我到那儿时，碰巧他不在。
= He happened to be out when I got there./ It chanced that he was out when I got there./ He was out by chance when I got there.
2. It seems/appears that sb. do/ be doing/ have done/ had done 似乎…, 好像…
= Sb. seems/appear to do/ be doing/ have done/to be done/to have been done
It seemed that he had been to Beijing before. 他好象以前去过北京。
= He seemed to have been to Beijing before.
3. It is / was＋被强调的部分＋that(who)+剩余的部分.
It wasn’t until he came back that I went to bed. 直到他回来我才睡觉。
It was because he was ill that he didn’t come to school today.