The marine cartilaginous fish that can produce electric current is
A. Torpedo
B. Trygon
C. Scoliodon
D. Pristis

Hint: Some species of cartilaginous fishes possess electric organs which are modified muscles that produce electric discharge in order to communicate, navigate or self defense. A fish that can generate the electric field is known as electrogenic.

Complete answer:
There are several species of electric fishes that can be found both in the ocean and freshwater. These fishes produce electric currents with the help of specialised electric organs which are a modified muscle or nerve cell that produce bioelectric fields which are stronger than the electric fields produced by the normal muscles or nerve cells. This electric organ is present in the tail of electric fish and the electrical output that it produces is known as the electric organ discharge. A strong electric discharge is used for the protection from predators and a mild electric discharge is used for communication and navigation. Weak electric discharge can be pulse-like which is highly variable with pauses or waves like periodic quasi-sinusoidal. Electric fishes include electric rays, electric eels and electric catfishes.
Torpedo is an electric ray having enlarged pectoral fins. They can produce an electric discharge of 8-220 volts depending on the species. They are also known as numbfish or crampfish and are the best known electric fishes. The name torpedo is derived from Latin word torpere which means to be paralysed or stiffened. This fish paralyses it prey or any organism that steps on it by mistake. They have a rounded pectoral disc on which pectoral fins are attached, dorsal fins and a stout muscular tail having a well-developed caudal fin. Their body is thick and flabby having soft loose skin without any thorns or dermal denticles. A pair of electric organs are present at the base of their pectoral fins which are kidney shaped.
Option B is Trygon which is also known as stingray as it has venom in its tail with which it makes a wound in its prey giving it a painful and life threatening experience. It has no relation with electric current.
Option C Scoliodon belongs to the species of sharks and has its body covered with placoid scales and has a spindle shaped body which is tapered at both the ends.
Option D Pristis is known as saw fish due to the presence of long, narrow, flattened nose extension lined by sharp transverse teeth making it look like a saw.

Hence, the correct answer is option (A).

Note: Electric rays have been used since ancient times to help humankind by numbing the pain during childbirth and other painful surgeries. They can produce the numbing effect without even touching the body of the organism.