We need two students____ (clean)the classroom.
They need help at the old ____ (people)home
Do you make any ____ (friend)here?
Mr.Wang teaches ____(they)math.
Sally is busy ____ (do)her homework.
污染居室环境的因素有:人体呼出的气体,排出的____ ,室内装饰材料释放出的有害物以及家用电器在使用过程中产生的____ 等.