含有Be动词(am is are was were)的句子,改一般疑问句,直接把Be动词提到句首.注意：主语是第一人称的,要把第一人称改为第二人称,如I-YOU WE-YOU ,人称改完后相应的BE动词也要发生变化.
解题步骤：（1）be动词提到句首：Are they doing their homework?
所以最后的答案为：Are they doing their homework?