—Look! The man welcoming us at the school gate ______ be our headteacher.
—No, it ______ be him. He is having a meeting in the office now.

(单选题)21. （ ） (单选题)______ understanding the challenges faced by the world’s poo (单选题)Nobody knows exactly how many years it will be ______ the Ch (单选题)______ is known to us is that the old scientist, for ______ (单选题)How dirty the tables are! They need ______ . (单选题)She said that she felt someone ______ in the room. (单选题)Please do your homework as ______ as ______. (单选题)He has few beautiful clothes, ______? (单选题)We had ______ the day before yesterday again. We have had __ (单选题)The Lion King is such ______ wonderful movie that I want to