Myofilaments or myofibrils are

Black bands of myofibrils are known as

In the myofibrils of muscle fibre:

In the center of each $I$-band is an elastic fiber called the $......$ which bisects it.

Sliding filament theory can be best explained as

Select the correct statement with reference to muscle structure.
$I.$ Each myosin is a polymerized protein.
$II.$ Many meromyosin constitute one thick filament (myosin).
$III.$ Each meromyosin's tail is called heavy meromyosin $(HMM)$ and head is called light meromyosin $(LMM)$.
$IV.$ The globular head is an active $ATPase$ enzyme and has binding sites for $ATP$ and active sites for actin.
Choose the option with correct statements.