In a relaxed muscle fibril,the $H$-zone,a lighter region of low density,can be seen in the centre of:

$I-$bands of myofibrils are bisected by

$A-$ Actin filaments occur in two forms: the monomeric $G$-actin and the polymeric $F$-actin.
$R-$ Tropomyosin is a rod-shaped fibrous protein. Tropomyosin forms two helical strands,which are wrapped around the $F$-actin filaments.

Which of the following statements is correct regarding muscle contraction?

Which one of the following events is thought to be most closely related to the sliding process between the two types of filaments which bring about contraction of the fibril?

Given below are two statements:
$Statement-I$: Plasma creatinine is produced during catabolism of creatinine phosphate in skeletal muscle contraction.
$Statement-II$: Creatinine phosphate provides a ready source of high-energy phosphate.
In the light of the above two statements, choose the most appropriate answer from the options given below.