The correct option could be (D):
The paragraph contains sentences that wander from the main topic.
The heading of the paragraph states that volunteering on a regular basis benefits one´s general physical health and supposedly the content of the paragraph should exemplify and detail some issues that support the main topic.
Nevertheless,many sentences detail situations not directly related with the main idea,e.g. examples of easy ways to integrate exercise into a daily routine, or how to combine minimal movement actions with some type of physical activity.