-Look at the picture on the wall. It         be David's.-Yes, his name is on the first page.

-　Look,　Sue　is　over　there.-　That　____　be　her.　She　is　in　Canada　now.

— I am going to spend my holiday in the countryside. — ________. The air there is fresh and the views are attractive as well.

--“Where is Tom?”--“He hasn’t come to school today, I think he ______be ill.”

— Where’s Lucy ? —  She ________ in the office. I saw her there just now.