______ well, you need to have a good sense of balance.

A．Danced

B．To dance

C．Dance

D．Dancing

结核杆菌在下列哪种情况下容易被消灭()

A．用青霉素

B．直接阳光下

C．暴露在空气中

D．在胃分泌物中

E．用强性肥皂