This question tests your ability to identify the relationship between pairs of words (analogy).

Analogy Reasoning

The first pair is 'AC : Cool'. An Air Conditioner (AC) is a device whose primary function is to cool a space. We need to find a similar relationship for the second pair, 'Heater : ?'.

Heater Function Analysis

A Heater is a device designed to produce or increase the temperature of something, essentially generating heat.

Evaluating Options

• Electricity: This is the power source for many heaters, not their primary output or function.
• Ray: While heaters might emit rays (like infrared), 'ray' is not the primary function itself.
• Heat: This directly corresponds to the primary function and output of a heater, similar to how 'Cool' is the function of an AC.
• Shine: This relates to light, which is not the primary function of a typical heater.

Therefore, the word that best completes the analogy is the one representing the core function of a heater.