If you often feel tired and can't focus your attention, that is________you have to stop working too

hard and to have a rest.[      ]

A. why  

B. whether  

C. when  

D. what

类风湿关节炎的关节症状是（）

A.对称性关节炎

B.侵犯小关节

C.关节附近的肌肉萎缩

D.出现晨僵

E.以上都是