Involuntary muscles are

When there is a drop in the force of contraction after prolonged stimulation,it is known as

Bone-dissolving cells are known as..........

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.

Actin filament is made up of

In a skeletal muscle fiber,how many actin filaments surround each myosin filament?