Identified the parts labelled as A , B , C and D in the given diagram.

The correct answer is Option (3) –

A-Actin binding sites
B-ATP binding sites
C-Head
D-Cross Arm

Each myosin (thick) filament is also a polymerised protein. Many monomeric proteins called Meromyosins constitute one thick filament. Each meromyosin has two important parts, a globular head with a short arm and a tail, the former being called the heavy meromyosin (HMM) and the latter, the light meromyosin (LMM). The HMM component, i.e.; the head and short arm projects outwards at regular distance and angle from each other from the surface of a polymerised myosin filament and is known as cross arm. The globular head is an active ATPase enzyme and has binding sites for ATP and active sites for actin.

                 Myosin monomer (Meromyosin)