I believe the answer is B. Free time
This is because, the word leisure refers to a quiet, peaceful, time to relax and do something you enjoy. This happens when there is nothing else to do, and you have free time to recuperate from daily stressors.
Although leisure time is quiet, this refers more to the free time you have to be somewhere quiet if you'd like.
Study time could work, however, studying isn’t always a peaceful relaxing time to read.
Learning could be a leisure activity but is usually more stressful than relaxing. Leisure can be engaging but shouldn’t be as demanding as learning.