The teacher ordered the classroom___at once and the students began to work .

A order sb to do sth.命令或嘱咐某人做某事.
参考
give instructions to or direct somebody to do something with authority
"She ordered him to do the shopping"请帮忙划一下句子成分!这句话是并列句，以and连接the teacher ordered the classroom to be cleaned at onceteacher 主语 order 谓语 the classroom 宾语 to be cleaned 宾语补足语 at once 应该是时间状语the students began to work students 主语 began 谓语 to work 宾语补足语