Sarcomere is the basic structural unit of the skeletal muscles. These sarcomere shows striations ( light and dark bands) when veiw under the microscope.
A band or anisotropic band is the dark region of sarcomere. A band consists of both thick and thin filaments of actin and myosin proteins. The A band has the ability to refract light and appears dark.
I’m pretty sure the answer is A because carbon dioxide causes a solution to turn yellow and a solution that indicates no carbon dioxide would be blue instead of green.