－ Whose is this blue bike? －It ________ be Mary’s. Her bike is black and white. 

This book _______ be Tom’s. Look! His name is on the cover.

It was fine yesterday so I ______ the trouble to carry my raincoat with me.

 – How’s your new class teacher?– We ______ ask for a better one. All my classmates love him so much.

—The research on the new flu virus vaccine is challenging and demanding. Who do you think can do the job?—________ my students have a try?