参考答案

正确答案：B
题意：咖啡因可用于……。
根据文章第二段倒数第一、二句As a component…caffeine increases their effectiveness and helps the body absorb them more quickly．By constricting blood vessels in the brain，it can alleviate head— aches可知，咖啡因有助于止痛药的吸收，且通过是脑内血管收缩能够缓解头痛，所以B项正确。根据文章第二段第一句many of caffeine’s undesirable effects，such as elevated…blood pressure可知，咖啡因使血压升高，而非降低，所以A项错误。根据第一段第三句Habitual coffee and tea drinkers…have a lower incidence of non—melanoma skin cancers和最后一句caffeinated coffee has also been associated with lowered risk of…liver cancer可知，咖啡因与降低患皮肤癌和肝癌的风险有关，而文章并未提及可用咖啡因来治疗肝癌与皮肤癌，所以C项和D项错误。故本题选B。