—Is there any vaccine(疫苗) against H1N1 flu that can be used on humans?
—No, but scientists are working to develop .
A. that
B. it
C. one
D. so
网友回答
A. that
B. it
(答案→)C. one
D. so
解析:考查指示代词。“有能够用在人类身上的,抵抗H1N1病毒的疫苗吗?”“没有,但是,科学家正在努力工作来研制一种。这里是泛指一种疫苗,应该用one。故选C。”