You are a research scientist. You are growing body parts and organs in the lab. First you grew some simple body parts like ears and noses. Then you tried bladders and blood vessels. You were successful! Now you want to try a heart! Your colleagues say it cannot be done because

A) the heart must move and it is not possible to make an organ that moves.
B) the heart is a pump made of muscle and that is difficult to grow in the lab.
C) the heart is made up of so many different types of cells that are organized into many tissues.
D) human hearts are not like any other animal hearts so there is not source for cells and tissues.