Step 1: A rectifier is a circuit, usually built from one or more diodes, that changes the type of current flowing through it.
Step 2: A diode conducts current easily in only one direction, called the forward direction, and blocks it in the reverse direction.
Step 3: Alternating current, or AC, keeps reversing direction periodically. When AC is passed through a diode, only the half cycle that forward biases the diode is allowed through, so the output current flows in one direction only, which is direct current, or DC.
Step 4: A device that does the opposite, DC to AC, is called an inverter, not a rectifier. Changing voltage level, high to low or low to high, is the job of a transformer, not a rectifier.
Answer: AC to DC, option B.