Question

living things ______ to changes in the environment. *
adapted
energy
stimulus
respond

Explanation:

Living things react to environmental changes. The term "respond" is the appropriate verb - form here. "Adapted" is past - tense and not in the correct verb form for this sentence structure. "Energy" and "stimulus" are nouns and do not fit grammatically as the verb needed to complete the sentence.

Answer:

D. respond