The line from the excerpt that best supports the idea that Ryan is an animal-lover is, He definitely would be back to visit the tamarins as soon as he could.
Because from the excerpt one can see the way Ryan treats tamarins, she is an animal lover. As in the excerpt, we can see she makes sure to double check the health of the tamarins and Ryan immediately understands what tamarins were and why they were called cotton-top tamarins, as each of them had a white tuft of hair on top of their heads.
Ryan just wanted to check their health and looked at their eyes, ears, and hands. It took 30 minutes for each tamarin, as she wanted to make sure they both had thorough examinations. And when the tamarin licked the end of his nose, Ryan laughed. He would definitely be back to visit the tamarins as soon as he could. All this supports the fact that Ryan is an animal lover.
Hence the correct option is, D. He definitely would be back to visit the tamarins as soon as he could.
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