It's difficult to keep track of all the rapid changes in technology.

keep 在这里是动词，意思是"保持、维持"。 track 是名词，原意是"轨迹、踪迹"，引申为"记录、跟踪"的意思。 keep track of 是一个固定短语，意思是"跟踪、掌握...的最新情况"，指持续关注并了解某事物的动态变化。