可使溃疡性结肠炎发作或加重症状的因素，以下应除外的是（）

A.饮食失调 

B.劳累 

C.药物 

D.精神刺激 

E.感染

“safe speed” is defined as that speed where（）.

A.you can stop within your visibility range

B.you can take proper and effective action to avoid collision

C.you are traveling slower than surrounding vessels

D.no wake comes from your vessel