When does the human body begin to lose vigor and the ability to function efficiently?

Đáp án A

Thông tin nằm ở đoạn 2: “Most body parts grow bigger and stronger, and function more efficiently during childhood. They reach their peak at the time of maturity, or early adulthood. After that, they begin to decline. Bones, for example, gradually become lighter and more brittle. In the aged, the joints between the bones also become rigid and more inflexible. This can make moving very painful.”