During the opening ceremony, "Miss Smile" has won the hearts of Chinese Internet users after being

caught ________ the same smile for nearly 20 minutes.[ ]

A. fixed  

B. to be fixed

C. to fix  

D. fixing

一类与种属无关的存在人、动物和微生物之间的共同抗原是（）

A.自身抗原

B.同种异型抗原

C.超抗原

D.独特型抗原

E.异嗜性抗原