variable/alternable/changeable factor可变因素:In the U.S., physical inactivity is the biggest changeable/variable/alternable factor, accounting for 21% of the risk for Alzheimer's, followed by depression and smoking.在美国,缺乏锻炼是最大的可变因素,占老年痴呆症风险的21%,排在其后的是情绪低落和抽烟。