Which condition represents the appropriate time for setting off distress flares and rockets? （）

A.Only when there is a chance of their being seen by rescue vessels

B.At half hour intervals

C.At one hour intervals

D.Immediately upon abandoning the vessel

幽门梗阻

A．血性呕吐
B．粪性呕吐
C．胆汁性呕吐
D．呕吐宿食伴酸臭味
E．喷射性呕吐