The correct answer is A) pass close together. The ARPA (Automatic Radar Plotting Aid) may automatically swap targets when two tracked targets pass close together. This is because when targets are in close proximity, the ARPA system may have difficulty distinguishing between the two and may inadvertently switch the tracking between the two targets. The other answer choices are incorrect because they do not describe a situation where the ARPA would be likely to swap targets. Targets being tracked at the same range, on reciprocal bearings, or on the same bearing would not necessarily cause the ARPA to swap targets in the same way as when the targets pass close together.