PAN-PAN repeated three times over the radiotelephone indicates which type of message will follow?（）

A.a ship is threatened by grave and imminent danger and requests immediate assistance
B.a calling station has an urgent message about the safety of a person
C.the message following the prefix will be about the safety of navigation
D.the message following is a meteorological warning

A.is 50% water saturated
B.is 90% water saturated
C.temperature is greater than the dew point temperature
D.temperature is equal to，or below the dew point temperature

A.in doubt that another vessel is taking sufficient action to avoid a collision
B.altering course to starboard
C.altering course to port
D.the stand-on vessel and will maintain course and speed