The correct answer is D) alternately flashing red and yellow light. According to the regulations for inland waterways, a commercial vessel engaged in public safety activities, such as law enforcement or emergency response, may display an identity light(s) that alternately flashes red and yellow. This alternating red and yellow light pattern helps to identify the vessel as being involved in public safety operations. The other options are incorrect because: A) alternately flashing blue and red is reserved for law enforcement vessels, B) a flashing blue light is used for emergency/rescue vehicles on land, and C) a flashing yellow light is typically used for warning or cautionary purposes, not public safety identification.