$ATPase$ enzyme needed for muscle contraction is located in

Select the true statement.

Endomysium is present in which of the following muscles?

Sarcoplasmic reticulum is related with

Rahul exercises regularly by visiting a gymnasium. Of late,he is gaining weight. What could be the reason? Choose the correct answer and elaborate.
$A$. Rahul has gained weight due to accumulation of fats in the body.
$B$. Rahul has gained weight due to increased muscle mass and loss of fat.
$C$. Rahul has gained weight because his muscle shape has improved.
$D$. Rahul has gained weight because he is accumulating water in the body.

Which of the following statements is correct regarding muscle contraction?