The answer for your question is G2!
Calcium ions presents Ca+ binds to troponin which makes tropomyosin move out of way for myosin to attach. Cross-bridge attaches. ATP breakdown provides energy to ready the myosin head for a power stroke. Myosin head attaches to exposed binding site on actin and the power stroke is accomplished. Cross-bridge (Myosin head) springs from raised position and pulls on the actin filament. Cross bridges break, ATP binds to Cross-bridge (but is not yet broken down) Myosin heads are released from actin. As long as calcium ions and ATP are present, this walking continues until the musle fiber is fully contracted. Hope this helps!
A vaccine promotes immunity by injecting the user with the virus or illness to help the body figure out what to do and thus build a defense from it hoped I helped (:
