I take in oxgyen from the air and send it into your bloodstream. I also remove the carbon dioxide from your body. What system am I? muscular system
respiratory system
digestive system
skeletal system please help

What rule is used to determine how many covalent bonds an element can form? a. the number of covalent bonds is equal to six c the number of covalent bonds is equal to five minus the group number plus the group number b. the number of covalent bonds is equal to eight d. none of the above minus the group number select the best answer from the choices provided