—Is there any vaccine(疫苗) against H1N1 f
题型:选择题
问题:
—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
—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