句型1
It (so) happened(chanced) that +clause. = sb. happened /chanced to do sth. =sb.did sth. by chance. 如：
It happened that he e to school today.只因为他有病了今天没有来上学。(只能用because而不能用for, as 或since)
It is I e back until the film ended. It manded /that +clause.(从句的谓语动词用should do, 但should可以省略。)如：
It is suggested that the meeting should be put off.有人建议推迟会议。
句型9
It is/es back.三个小时之后他才能回来。
句型14
It is +形容词(possible, impossible, necessary等) +for+ sb.+ to do. 如：
It is impossible for me to finish this work before tomorrow.我明天之前完成此工作是不可能的。
句型15
It is +(心理品质方面的)形容词+of + sb. +to do.= 主语+ be +形容词+to do.(常用的形容词有：kind, stupid; foolish, good, wise等。)如：
It is kind of you to help me.=You are kind to help me.你真好给我提供了帮助。