问题：
For drinks containing caffeine, ______ is consider
答案：
half the bottle解析:根据题干的关键词drinks,caffeine,appropriate quantity定位到原文倒数第二段最后一句:The directions also advise people to limit caffeine products and to drink only half the bottle which is regarded as a moderate amount.可知使用说明建议人们减少饮用含咖啡因的饮料,而且合适剂量应该是半瓶。题干中的appropriate quantity与句中的moderate amount是同义转换。