John & Peccavi both wish to know why you are asking such a strange question?
We also believe the correct answer is both A) and D)
The relay disconnects the generator from the battery...
If the engine makes the generator run very quickly the output voltage may be too high and damage the battery
If the engine runs very slowly (or not at all) the battery will discharge itself through the generator (try to run it like a motor)
Both situations are best avoided...
Peccavi, June 2009
