In frogs,mucus helps to keep the skin ..........

The skull of a frog is . . . . . . .

The number of spinal nerves in a frog is......... (in $pairs$)

Choose the correct sentences for a female frog.
$1$. Vocal sacs are absent in female frogs.
$2$. $A$ mature female can lay $2500$ to $3000$ ova at a time.
$3$. In female frogs,fertilized eggs are encased in oothecae and it is a dark reddish to blackish brown.

Select the correct option for the nervous system of a frog.

Frogs differ from humans in terms of: