The correct option is A HMM
Each meromyosin has two components, namely HMM and LMM. HMM has a globular head part and short arm LMM, which is the tail part. HMM is involved in the formation of cross arm during the muscle contraction. Its components are projected at regular intervals, forming angle with each other. Head part is the active ATPase enzyme and can bind to ATP. So we can say that the formation of cross arm bridge is due to the presence of HMM.