Final answer:
If a 56-kg woman wants to maximize calorie burn while swimming, she should choose backstroke or slow crawl, and not treading water, as these strokes burn more calories in a 30-minute session.
Step-by-step explanation:
If a 56-kg woman wants to burn the most calories through swimming, the best option for her is not treading water but rather utilizing different strokes that have higher calorie usage. According to the data in the question, the strokes that allow a 56-kg woman to use the most calories are the backstroke and the slow crawl, both yielding 95 calories burned for 30 minutes of swimming. In contrast, treading water only leads to burning 35 calories in the same amount of time for a woman of the mentioned weight class.