Which protein is distributed at regular intervals on the tropomyosin protein?

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 visceral muscles?

Which mineral element is essential for muscle contraction?

The diagram given below represents the structure of a striated muscle fiber. Label the parts $A, B, C, D, E$ and $F$.

Analogy type questions:
$(1)$ Red muscle fibers / White muscle fibers have fewer mitochondria but more sarcoplasmic reticulum.
$(2)$ When nerve impulses reach the neuromuscular junction,acetic acid / acetylcholine neurotransmitter is released.