Answer: D
In order to improve abdominal endurance, Jamie must change her workout by lowering the resistance or weight of the object she use with higher repetitions of 12 to 18 repetitions per set. This way, she can condition herself into higher repetitions and eventually sustain longer activities.
Moreover, Jamie can use stability ball crunches as a simple way to build endurance in the rectus abdominis. Some other crunches she may use would include elevated leg crunches and reverse crunches. Furthermore, she may add the plank holds, side plank and two-limbed plank in her routine to fully achieve her workout goal.