$Ca^{2+}$ is required in which of the following processes?

Write true or false. If false,correct the statement to make it true.
$(a)$ Actin is present in thin filament.
$(b)$ $H$-zone of striated muscle fibre represents both thick and thin filaments.
$(c)$ Human skeleton has $206$ bones.
$(d)$ There are $11$ pairs of ribs in man.
$(e)$ Sternum is present on the ventral side of the body.

Locomotion requires a perfectly coordinated activity of:

Which one of the following pairs of structures is correctly matched with their description?

Description	Structures
$a$. Tibia and fibula	Both form parts of knee joint
$b$. Cartilage and cornea	No blood supply but do require oxygen for respiratory need
$c$. Shoulder joint and elbow joint	Ball and socket type of joint
$d$. Premolars and molars	$20$ in all and $3$ rooted

Identify the parts $A$ and $B$ from the given diagram.

Which of the following is not a function of the skeletal system?