When one perspires heavily this is the integumentary system at work. The integumentary system includes your skin and glands that aid in sweating.
When one digests food the digestive system is at work. The digestive system includes the stomach, esophagus, mouth, intestines.
When one takes a breath the respiratory system, which is composed of the lungs, is at work.
When one stands up the skeletal muscle system are at work.
D is the correct answer
Hope this helped!
~Just a girl in love with Shawn Mendes