Explanation
Correct answer: A.
Choice A is the best answer. The text says that corals produce bright colors to block sunlight and encourage algae to recolonize after “an environmental stressor.” From this, we can infer that corals that produce bright colors have probably been subjected to an environmental stressor.
Why the other choices are wrong
Choice B
Choice B is incorrect. The text says that corals produce bright colors to block intense sunlight, which protects the light-sensitive algae that keep the coral healthy. In other words, bright colors make the coral’s health less vulnerable to intense sunlight.
Choice C
Choice C is incorrect. The text says that corals produce bright colors to encourage algae to recolonize, not that they have recovered without the assistance of algae colonies.
Choice D
Choice D is incorrect. The text never compares the likelihood of differently colored corals surviving without algae colonies.