— Your brother isn't at home. Where is he? 

— He _____ to Beijing. He _____ for over 2 months. [ ]

A. has been; has left

B. has gone; has gone

C. has gone; has been away

将0.5g二氧化锰与一定量氯酸钾共热到质量不减少为止，称得残渣质量为15.4g。求：

（1）生成氧气多少克？

（2）原先氯酸钾的质量是多少克？