Question

When electric current is flowing in a circuit, if the voltage applied to the circuit is increased,

Answer 1

     The currente of a circuit is given by First Ohm's Law:

$i= \frac{V}{R}$
 
     Therefore, if the voltage increased, the resistence must also increase, so that the current remains constant, otherwise the current will increase.

Letter B
 
     If you notice any mistake in my english, please let me know, because i am not native.

Answer 2

The current that flows in the circuit is

      (voltage applied to the circuit)
divided by
      (net resistance of the circuit) .

The resistance of most circuits is constant.  So this simple formula
shows that the current is directly proportional to the applied voltage. 
If the applied voltage increases, so does the current.