1.The human body is capable of a great variety of physical activities. 2.With training, some individuals can run a mile in less than four minutes, or lift more than their won weight. 3. Sensitive motor skills allows us to thread a needle, turn our head to focus on a single star, and throw a baseball into the strike zone. 4. Considered individually, any one of these activities may not seem amazing. 5. However, for a single structure (the human body) to be capable of all of them is remarkable indeed. Which sentence is the topic sentence?