选is(因为后边的回答已经提示了,回答用的是is,假设你对划线部分“the boy”提问的话,当然也要用is)相当于:Who is this boy and (who is) this girl?是分开的。句子中,who做表语。例:What is your given name?What--表语,is-- 系词,your given name--主语
are, 因为句子的主语是this boy and this girl, 回答;This boy and this girl are......, 所以who是表语