—What happened to your classmate Jane?                      

—She _____ the bicycle when she practiced it yesterday and _____ her leg and arm.               [ ]

A. fall down, hurt

B. fell down, was hurt

C. fell off, hurt

某钢瓶内装有一定量的氧气，一次电焊中用去其中的1/3，则瓶内剩余氧气的质量是原来的________倍，密度是原来的_________倍。