Which of the following marine cartilaginous fishes produces an electric current?

$Pristis$ belongs to the class:

In which of the following organisms does the heart pump only deoxygenated (impure) blood?

Which of the following characteristic features always holds true for the corresponding group of animals?

Select the incorrect statement regarding the evolution of the heart.

Which of the following statements are not true about shark?
$a$. The skin is tough and covered with placoid scales
$b$. They possess a swim bladder which regulates buoyancy
$c$. The tail of shark is heterocercal
$d$. Ampulla of Lorenzini present in the snout of shark is a thermoreceptor.
$e$. It has five pairs of gill slits covered by operculum