Final answer:
The correct option for Amber's exercise intensities during the fourth, fifth, and sixth visits is to increase the intensity compared to the first three visits, aligning with the program's pattern of gradual progression.
Step-by-step explanation:
According to the described exercise program, the possible intensities for Amber's exercise during the fourth, fifth, and sixth visits should involve increasing the intensity compared to the first three visits. The program suggests a pattern of maintaining intensity at first, then gradually increasing it, followed by a decrease before repeating the pattern. Therefore, for Amber's fourth to sixth visits, the correct option out of the provided ones would be the second option, which is Increasing the intensity compared to the first 3 visits.