Question

—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

Answer 1

C

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。”