Study the following sentences:
$I.$ The accumulation of pyruvic acid in the muscle causes fatigue.
$II.$ $ATP$ is resynthesized in the muscle by the phosphorylation of $ADP$ by a phosphogen.
$III.$ Cori cycle involves muscles and liver.
$IV.$ The phosphogen in the vertebrate muscle is arginine phosphate.
The correct set of statements regarding muscle contraction is:

$A$ femur is kept in dilute $HCl$ for three days,it becomes

$A$: On repeated application of stimuli,involuntary striped muscles undergo fatigue.
$R$: This is due to non-availability of $ATP$ molecules.

Fill in the blank spaces:
$(a)$ All mammals (except a few) have ............. cervical vertebra.
$(b)$ The number of phalanges in each limb of human is ............. .
$(c)$ Thin filament of myofibril contains $2 \,'F'$ actins and two other proteins namely .............. and ........... .
$(d)$ In a muscle fibre $Ca^{++}$ is stored in ............. .
$(e)$ .............. and .............. pairs of ribs are called floating ribs.
$(f)$ The human cranium is made of .............. bones.

Match List-$I$ with List-$II$.

List-$I$	List-$II$
$(a)$ Scapula	$(i)$ Cartilaginous joints
$(b)$ Cranium	$(ii)$ Flat bone
$(c)$ Sternum	$(iii)$ Fibrous joints
$(d)$ Vertebral column	$(iv)$ Triangular flat bone

Choose the correct answer from the options given below.

In children,the bones are more flexible and less brittle because their bones have: