Muscles in animals are often found in pairs, because a muscles can produce a force as they relax b muscles can only pull c muscles can only pull d muscles need to be able to both push and pull

B muscles can only pull 

A type of a balanced stretch involves targeting a specific muscle group. When stretching, a person should be aware of the agonist and antagonist muscles being stretched in able to create a balance between the joints where the muscles are attached. Stretching is an important phase in the exercise cycle and should not be missed as this prevents injuries in the joints and increases the blood flow into the muscles that were used during the activity. Stretching also contributes to lessening the lactic acid build up that happens during physical activity.