The correct answer is B) 2 B-I portable fire extinguishers. According to the uninspected vessel regulations, a 45-foot motorboat with a fixed fire system on board is required to have a minimum of 2 B-I portable fire extinguishers. This is because the fixed fire system is considered one of the required fire extinguishers, and the regulations mandate an additional 2 B-I portable extinguishers for vessels of this size. The other options are incorrect because A) 1 B-I is not enough, C) 3 B-I is more than the required minimum, and D) 4 B-I is also more than the minimum requirement.