What does it mean to 'fortify' something?

To 'fortify' something means to strengthen or build it up. This term is often used in various contexts, such as in military strategy where a position is fortified with defenses to protect against an attack, or in nutrition, where food products may be fortified with vitamins to enhance their health benefits. The core idea behind the word is about making something stronger or more robust, whether it be physically, mentally, or in terms of structure. This term implies an enhancement, making it more resilient against challenges or adversities.

The other options do not align with this meaning. Weaken or diminish indicates a reduction in strength, clarify suggests making something clearer without any implication of strength, and alter or change significantly implies modification rather than enhancement. Thus, strengthening or building up is at the heart of the correct answer.