We can easily find out the beginning point of the line by using dot representation. When it comes to position vector, it expresses the exact position of certain object from the starting point of the coordinate system. The vector is a straight line that has a certain end which is fixed to its body.
Red blood cells contain enormous amounts of a protein called hemoglobin. This iron-containing molecule binds oxygen as oxygen molecules enter blood vessels in the lungs. Hemoglobin is also responsible for the characteristic red color of blood.
You can automatically eliminate B and D because they have little to do with the movement of the body. And it's not A because the skeletal system doesn't have the signals to tell the muscular system what to do.
