Physical activity is distinct from exercise because it may include activities that are

Physical activity is any activity that you may do that helps to improve or maintain your physical fitness as well as your health in general. Exercise is any activity requiring physical effort, carried out especially to sustain or improve health and fitness.

Bmust be the answer, as technically all organs move, so a is incorrect. all organs are made of different types of cells, so that isn’t a problem, so c is also incorrect. human hearts are very similar to many other animals’ hearts, so d is also incorrect, yet the heart is made of muscle, which is hard to grow in the lab so it would be correct to say b