If an airplane circles a vessel 3 times，crosses the vessel’s course close ahead while rocking the wings，and heads off in a certain direction，what does this indicate?（）

A.The plane is in distress and will have to ditch

B.The plane is going to drop a package and wishes the vessel to recover it

C.Someone is in distress in that direction and the vessel should follow and assist

D.There is danger ahead and the best course is indicated by the direction of the aircraft

开放性骨折清创术中伤口周围及手术部位的全部皮肤一般要刷洗（）。

A.1次

B.2次

C.3次

D.4次

E.5次