从一问一答可以看出,前句是对职业的提问.对职业提问一般不用who,可用what are they?或者what do they do?或者是what are their jobs?
Who are they 意为他们是谁,他们都有谁等等,也可以表示询问职业,但很少用.通常回答是如:（they are Jack,Tom and Jim）、（they are teachers of our Middle school）.之类.