The correct answer is B) when the ship's generators have been disconnected from the main bus. The reasoning behind this is that it is the safest time to close the shore power circuit breaker because the ship's generators are not connected to the main bus. This ensures there is no risk of a power surge or backfeed from the ship's generators into the shore power system, which could be hazardous. The other options are incorrect because A) closing the shore power circuit breaker at any time in a shipyard may not be safe if the generators are still connected, C) directly paralleling the ship's generators to those on shore before closing the circuit breaker creates a risk of power surges, and D) the use of a quick disconnect coupling does not eliminate the need to first disconnect the ship's generators.