When operating the air supply system in a covered lifeboat the（）.

A.fuel supply valve should be closed

B.hatches，doors，and oar ports should be closed

C.air cylinder shut-off valve should be closed

D.engine should be shut off

三角帆蚌的气单胞菌病的症状与病理变化特点描述不正确的是（）

A.闭壳肌松弛，蚌壳后缘出水管喷水无力

B.呼吸频率降低，体内有大量黏液流出

C.病蚌肝小管肿大破裂

D.外套膜边缘的贝壳突起变形、萎缩