focus用法：当作为动词时，意为集中、调节焦距、集中、聚焦，常与介词on连用，表示聚焦于”、致力于”；作为名词时，意为中心点、焦距、调焦、焦点、源等。
一、作为动词，意为集中(注意力、精力等于);(使)调节焦距;集中(光束于);聚焦(于)；与介词on/upon连用。
例句：The discussion focused on three main problems.
讨论集中在三个主要问题上。
Each exercise focuses on a different grammar point.
每个练习各有不同的语法重点。
It took a few moments for her eyes to focus in the dark.
过了好几分钟她的眼睛才适应了黑暗。
I quickly focused the camera on the children.
我迅速把照相机的镜头对准孩子们。
The visit helped to focus world attention on the plight of the refugees.
这次访问促使全世界关注难民困境。
二、作为名词，意为中心点(指人或事物);(眼睛或镜头的)焦距，调焦;(光、声等的)焦点，中心点，源。
例句：It was the main focus of attention at the meeting.
这是会议上关注的主要焦点。
The incident brought the problem of violence in schools into sharp focus .
这次事件使校园暴力成为焦点问题。
The binoculars were not in focus.
这副双筒望远镜的焦距不对。
The new system is the focus of controversy
这个新体制是争议的焦点。
