They do what they can to help others.为什么不是They do what they can do to help others?what they can 是什么成分?为什么不要加第二个do?

what do they do they what do they do? They shall do what they what()they()they()there?what()they()they()there?[do] what do they What do they what do they What do they need? what animals do they they/have/what/do/(?) what do they what do they do?(工程师) do they say what they would What do they doing?是What do they like doing？ What can't they do　还　 what they cant do? What ___ do they like? What are they( )(do)now what will they do firt