Final answer:
Electric heaters and steam injection are the elements used for heating bubble and passover humidifiers.
Step-by-step explanation:
The elements used for heating bubble and passover humidifiers are electric heaters and steam injection. In bubble humidifiers, a heating element (usually electric) heats the water to create steam, which is then released into the air. Passover humidifiers, on the other hand, use steam injection to create a mist of water particles.