The 650 skeletal muscles in the human body contract when they receive signals from motor neurons, which are triggered from a part of the cell called the sarcoplasmic reticulum. Motor neurons tell your muscles to contract and the better you become at having those signals tell your muscles to contract, the stronger you can get.
I believe it is A because i feel it is the only exercise were you are using your arms to lift you entire body off the ground, but who knows i could be wrong <span />
