The correct answer is B) -2s. The chronometer rate is the difference in time between the chronometer's reading and the actual time. In this case, the chronometer read 11h 59m 59s at the 1200 GMT time tick yesterday, but it read 11h 59m 57s at the 1200 GMT time tick today. This means the chronometer is running 2 seconds slower than the actual time, hence the chronometer rate is -2s. The other options are incorrect because: A) +2s would mean the chronometer is running 2 seconds faster than the actual time. C) -3s would mean the chronometer is running 3 seconds slower than the actual time. D) +3s would mean the chronometer is running 3 seconds faster than the actual time.