Final answer:
The correct sentence uses the comparative form of an adjective by adding the suffix '-er' to the end of the adjective.
Step-by-step explanation:
The correct sentence that uses the comparative form of an adjective is:
'Every time I see a rainbow, it seems to be more colorful than the last one.'
In this sentence, the comparative form of the adjective 'colorful' is used correctly by adding the suffix '-er' to the end of the adjective. This is the standard way of forming the comparative form of most one-syllable adjectives.
For example, the adjective 'big' becomes 'bigger' in the comparative form, and the adjective 'fast' becomes 'faster' in the comparative form.
Learn more about comparative form of adjectives