Explanation
Correct answer: D.
Choice D is the best answer. The author of Text 2 acknowledges that nanohybrids may be more toxic than their constituent parts, but also provides an example of a nanohybrid that has reduced toxicity compared to its components: silicon dioxide and zinc oxide together have all the benefits of zinc oxide nanoparticles without any of the DNA harm zinc oxide has on its own.
Why the other choices are wrong
Choice A
Choice A is incorrect. While the author of Text 2 gives an example of a nanohybrid that isn't as toxic as its constituent parts, they don't argue that the benefit outweighs the risk. They merely argue that "the effects of nanomaterial conjugation vary by case."
Choice B
Choice B is incorrect. The author of Text 2 states that the effects of nanomaterial conjugation "vary by case," and that the attention that their potential toxicity has drawn is warranted. If the situation in Text 1 weren't representative, then there would be less attention to the potential danger of these materials. Furthermore, neither passage suggests that researchers had expected that they could predict the effects of nanomaterial conjugation.
Choice C
Choice C is incorrect. The author of Text 2 agrees that the potential toxicity of nanohybrids "has drawn deserved attention," so they aren't denying the problem.