The answer is b.
Arc blow is defined as the deflection of the arc by means of the magnetic fields set up due to the flow of the welding current.
The result of an arc blow is an excessive spatter (throwing out the tiny droplets of the weld metal out of this joint on to the base metal which appear as the tiny dots on the metal plates. The problem of the arc blows gets multiplied when welding is done on the strongly magnetic materials such as the nickel alloys because of the strong magnetic fields set up by these metals. Arc blow problem is faced with the dc arc.
In the shielded metal arc welding on the direct current, arc blow is caused by the magnetic field, that deflects the arc force and puddle from its normal desired direction.