——Tom is never late for work. Why is he absent today?

—— Something _____to him.

A．must have happened

B．can have happened

C．must happen

D．can happen

某6周龄肉鸡群中部分鸡出现跛行，卧地懒动，跗关节肿胀，关节囊及腱鞘水肿，关节腔内有浅黄色渗出物。该病最可能的诊断是（）

A.鸡传染性支气管炎

B.鸡病毒性关节炎

C、禽白血病

D、禽霍乱

E、传染性法氏囊病