Which of the following statements is TRUE regarding automatic identification systems (AIS) ?（）

A. The master may，at his/her discretion，turn off the AIS if he/she believes that it may compromise the safety or security of the vessel
B. Under no circumstances shall AIS be turned off while underway as this could endanger the vessel and those around her
C. AIS is always required to be operating if the vessel is in or in the vicinity of a VTS area
D. AIS is always required to be operating if the vessel is within 100 nautical miles of the coastline