Answer is C.
Components connected in parallel are connected so the same voltage is applied to each component. In a parallel circuit, the voltage across each of the components is the same, and the total current is the sum of the currents through each component.
In this case, 3 identical bulbs are connected in parallel. Therefore, the voltage remains the same across each bulb but the current is equally shared by all the three bulbs, that is, each bulb needs 2 A of current out of total 6 A as given in the question.
When one bulb, is fused out, only bulbs burn and only 4 A current is used.
Hence, the total current drawn from the battery when one bulb fuses is 4 A.