Which type of scales are found on the skin of cartilaginous fishes?

Which one of the following groups of animals is correctly matched with its characteristic feature without any exception?

Which of the following animals possesses an endoskeleton made entirely of cartilage?

Cartilaginous fishes (Class $Chondrichthyes$) are characterised by the presence of:

Teeth are modified . . . . . . scales which are backwardly directed.

Which of the following statements are not true?
$a$. Dermal scales of fishes form the exoskeleton.
$b$. Cycloid and ctenoid scales have distinct lines of growth which aid in determining the age of the fish.
$c$. Fish scales are never shed.
$d$. The skin in elasmobranchs is covered with placoid scales.
$e$. The development of a placoid scale is not like the development of a tooth.