The correct answer is A) 16. Marine operators normally call ships on VHF-FM radiotelephone channel 16, which is the international distress, safety, and calling channel. This channel is designated for hailing and establishing contact with other vessels. Once contact is made, the conversation would typically be switched to a different working channel to avoid congestion on the distress/safety frequency. The other answer choices are incorrect because: B) Channel 13 is typically used for bridge-to-bridge communications, C) Channel 23 is not a standard maritime VHF channel, and D) Channel 19 is often used for working communications on inland waterways, but is not the standard hailing channel.