Which statement about entry into a water ballast tank that has been sealed for a long time is TRUE?

Correct Answer: Option C — After ventilation and testing, and the tank is found safe for entry, someone should standby at the tank entrance while you are inside.

Enclosed space entry procedures require a designated standby person stationed at the entrance at all times once the space is deemed safe and ventilated. The buddy system applies to those entering, not a single standby guard.