People thought __necessary to invite Mr Smith to speak at the meeting
答案：it
翻譯：人們認(rèn)為邀請(qǐng)Mr Smith在會(huì)議上眼睛很有必要.
解析：it做形式賓語(yǔ),真正的賓語(yǔ)是to invite Mr Smith
It was some time __ we realized the truth
答案：until
翻譯：在我們認(rèn)識(shí)到真相以前花費(fèi)了一些時(shí)間
解析：根據(jù)句子意思使用until
Sandy could do nothing but__to his teacher that he was wrong(admit)
答案：admit
翻譯：Sand除了向老師承認(rèn)他的錯(cuò)誤以外什么事情也做不了
解析：but當(dāng)除了講,后面使用to do,但是當(dāng)but前面有do以及do的各種形式,后面省略to,直接加動(dòng)詞原形.