At sea，you are approaching a small vessel and see that it has the signal flag P hoisted. What should you do?（）.

A.Proceed on present course and speed since the vessel is stopped and making no way through the water
B.Keep clear of the vessel because it has a diver down
C.Attempt to call the vessel on VHF radiotelephone because someone on board requires medical assistance
D.Approach with caution because the vessel is a fishing vessel and its nets are fouled on an obstruction