With three resistances connected in parallel, if each dissipates 20 W the total power supplied by the voltage source equals

The correct answer is D. 60 W.

The total power dissipated by three resistances connected in parallel is equal to the sum of the power dissipated by each resistance. In this case, each resistance dissipates 20 W, so the total power dissipated is 20 W + 20 W + 20 W = 60 W.

Option A is incorrect because it is the power dissipated by a single resistance. Option B is incorrect because it is the power dissipated by two resistances. Option C is incorrect because it is the power dissipated by three resistances in series.