In summer，food will go bad if ________ in room temperature[ ]

Why do you admire Mr. Hu so much— Because he is the person ______ helps us learn much knowledge.

Where was your mother when the rainstorm came yesterday—She _________ dinner in the kitchen.

______useful dictionary for beginners ofEnglish! Where did you get it?

Had it been possible I would have gone to the movies but I _____ too busy.[ ]