Answer:
Skeletal system
Step-by-step explanation:
Think about it, your bones are hard. This helps with structure and support of your body. Your nervous system deals with your brain so that isn't it. Your digestive system is your stomach and all that good stuff, but it's job is processing food! So that's not it either. Then, last but not least, your circulatory system deals with your heart and blood and stuff. So, while yes, all of these systems are important, your skeletal system is what keeps you upright lol Hope this helps! Good luck!