同学你好，该知识点来自沪江网校《高中水平直达托业目标800分丨新题型随到随学优选班》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好
pledge: 保证；诺言；誓约 (较为严肃的保证)
a pledge of support
支援的许诺
Management has given a pledge that there will be no job losses this year.
资方保证今年不会削减工作职位。

promise: 许诺；承诺；答应；保证
to tell sb that you will definitely do or not do sth, or that sth will definitely happen
The college principal promised to look into the matter.
学院院长答应研究这个问题。
‘Promise not to tell anyone!’ ‘I promise.’
“你要保证不告诉别人！”“我保证。”

obligation：义务；职责；责任
You are under no obligation to buy anything.
你不必非买什么东西不可。
She did not feel under any obligation to tell him the truth.
她觉得没有义务告诉他实情。

engagement：（尤指正式的或与工作有关的）约定，约会，预约
an engagement book/diary
预约簿 / 日志
He has a number of social engagements next week.
他下周有几次社交约会。