o­nitrobenzyl (ONB). When they catch the light, ONB groups fall off the polymer, leading to its breakdown. But ONB is only a so­so NIR absorber, and it could be poisonous to cells when it separates from the polymer.

　　So Almutairi and her colleagues reported creating a new material for capsules that's even better. This one consists of a long chain of compounds called cresol groups linked in a polymer. Cresol contains reactive (易反应的) components that make it highly unstable in its polymeric form, a feature Almutairi and her colleagues use to their advantage. After polymerizing the cresols, they cap each reactive component with a light­absorbing compound called Bhc. When the Bhcs absorb NIR light, the reactive groups are exposed and break the long polymer into two short chains. Shining additional light continues this breakdown, potentially releasing any drugs in the capsule. What's more, Almutairi says, Bhc is 10 times better at absorbing NIR than is ONB and is not poisonous to cells.

　　63. According to the passage, which of the following could be the best trigger?

　　A. Temperature change.

　　B. NIR light.

　　C. Acidity change.

　　D. UV light.

　　64. Why is ONB unsatisfactory?

　　A. It breaks down when it absorbs NIR light.

　　B. It falls off the polymer and triggers drug release.

　　C. It has not come onto the market up till now.

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