The correct answer is B) generally steady bearing and decreasing range. This is correct because under both the International and Inland Navigation Rules, the risk of collision exists when an approaching vessel is observed to have a generally steady bearing and a decreasing range. This indicates that the two vessels are on a collision course and must take appropriate action to avoid a collision. The other options are incorrect because: A) Increasing range and bearing indicates the vessels are moving apart and not on a collision course. C) Decreasing bearing only indicates the vessels are passing each other safely and not on a collision course. D) Generally steady range and increasing bearing indicates the vessels are moving away from each other and not on a collision course.