咱们先看句子的主体结构:“Understanding what distinguishes people who battle with Alzheimer's as they age from those whose mental acuteness remains strong well into their 80s,90s and even older”是主语,“is a major focus of current psychiatric research”是谓语。这句话主要表达的是“理解某种区别是当前精神学研究的重点”。 然后分析这个主语部分的复杂结构: “people who battle with Alzheimer's as they age”指的是那些随着年龄的增长而患有阿尔茨海默症的人; “those whose mental acuteness remains strong well into their 80s,90s and even older”指的是那些即使到了80岁、90岁甚至更高龄时仍能保持思维敏捷的人; “what distinguishes ... from ...”是一个关系代词引导的宾语从句,用来描述上述两类人之间的区别。