—Who helped you repair your bike?

—______! I repaired it all by myself. [ ]

A. Everybody

B. Anybody

C. Somebody

D. Nobody

能特异地与原核生物RNA聚合酶β亚基结合的抗生素是

A．氯霉素
B．利福霉素
C．卡那霉素
D．嘌呤霉素