A skier can react to an obstacle in the water using all three of these system.
Nervous system - sends the visual signal to the brain so the brain can process and send a signal to the muscles.
Muscular system - takes the signal from the nervous system and the muscles provide movement to get away from The obstacle.
Skeletal system - the skeletal system is next to the muscular system and when the muscles react, the bones from the skeletal system are connected and provide the structure needed to move away from the obstacle.
All three systems are necessary!