—Alex's already gone back to Australia, _________?

—_________. He is on a visit to Shanghai.[ ]

A. isn't he; No  

B. hasn't he; Yes  

C. isn't he; Yes  

D. hasn't he; No

在加热炉扫线过程中，为防止炉管存水，扫线结束后，必须先用（）赶水。