serve n. 原因；理由
(1) 为……服务／工作 A slave serves his master.
(2) 接待(顾客) The shop assistant is serving a customer.
(3) 侍候吃饭，端(菜)；供应(饭菜)
Lunch is served now.
(4) serve as 充任(某职务)作……用
She served as a model for several painters.
This box will serve as / for a seat.
人教版高一英语单词精讲：role
role n. 原因；理由
(1) (戏剧中的) 角色
Oliver played (acted) the role / part of Hamlet.
(2) (现实生活中的) 身份；作用
What is your role on the Committee?
(3) play a...role in... = play a...part in在……中扮演……角色或作用
The headmaster plays an important role / part in the good running of a school.
人教版高一英语单词精讲：reason
reason n. 原因；理由
(1) + to do sth. You haven't any reason to leave me.
(2) + for sth. / doing People must have a reason for saying such things.
(3) + 从句；从句用why / for which引导 That is the reason why you should leave.
(4) for + reason，为了某种原因He is retiring for reasons of health.
[比较] cause“原因；起因”
the cause of the fire 火灾的起因(引起某种后果的起因)
the reason for being late 迟到的理由(做某件事的理由)
