Read the excerpt from "On Becoming an Inventor" by Dean Kamen. When I was twelve years old and Barton, my older brother, was around fifteen, we took over the family basement. At first, I made a darkroom for developing pictures, and Bart was using it as his lab where he was raising about one hundred white rats, removing their thymus glands, and trying to figure out the glands' dysfunction. He wanted pictures taken of his experiment, doing the surgery on rats, and since I already had a darkroom, I took the pictures, though somewhat reluctantly. I didn't like the blood. Which part of the excerpt expresses an opinion? we took over . . . I made a darkroom for developing pictures . . . he was raising about one hundred white rats . . . I didn't like the blood.