---------Where is Mr Li?

----------He ___________in the office. I saw him leave just now.

A．must work

B．can’t be

C．might be

D．must be working

某含铁样品5.6g与足量稀硫酸完全反应后产生氢气0.195g，则其所含杂质可能是（　　）

A．Na

B．Mg

C．Al

D．Zn