At the time of short circuit, the electric current in the circuit :(a) vary continuously (b) does not change(c) reduces substantially (d) increases heavily

When the plastic insulation of live and neutral wires gets torn somehow and touches each other, then due to this direct touching (connection) of the two wires an electric short circuit occurs.  The resistance of the circuit so formed is very small, therefore, the current flowing through the wires increases heavily.