The correct answer is: A. Decrease
When the resistance element of a heater fuses, the power of the heater will decrease. This is because the resistance of the heater is what causes it to heat up. When the resistance is decreased, the amount of heat that is generated is also decreased.
The resistance of a conductor is proportional to its length and inversely proportional to its cross-sectional area. When a portion of the resistance element is removed, the length of the conductor is decreased, which causes the resistance to decrease. This decrease in resistance causes the power of the heater to decrease.
Option B is incorrect because the power of the heater will decrease, not increase. Option C is incorrect because the power of the heater will decrease, not remain constant. Option D is incorrect because the power of the heater will decrease, not none of the above.