U
　　50．●undertake (undertook, undertaken)  v. 承担，从事，负责；承诺
　　undertake the difficult task/responsibility
　　undertake to do           He undertook to finish the job by Friday.
　　51. ◎unfair
　　an unfair judge
　　be unfair on/to sb
　　It's ~ on him to make him pay for everything.
　　He is ~to us, isn't he ?
　　52. ● unite  v. 联合，团结
　　Carnival became a way to unite different communities.
　　We should unite with all the forces that can be united.
　　53. upon prep. 在… 上面
　　upon /on+ sth/doing  名词/动名词= as soon as 从句
　　Upon his arrival, I will telephone you.
　　54. ●upset  a. 心烦的，苦恼的
　　Then the friend went away, and the writer was extremely upset.
　　be upset to do sth:    She was upset to hear that the holiday had been cancelled.
　　be upset that clause:   Her sister was very upset that her family had to move to California.
　　be upset about/over sth: My parents were in a huge argument, and I was really upset about it.
　　55. ●urge  vt. 鼓励，激励
　　urge sb to do/into doing      They urged me to eat the strange food.
　　urge that clause(should do)   He urged that we should take such steps.
　　56. use  n. 利用，用途；v. 利用
　　make (good/ better/full) use of sth （好好/充分）利用某物
　　sth be in use/ out of use 某物在被使用/ 某物不被使用
　　sth come into use 开始被使用
　　It is no use doing.干某事没用
　　be/get used to n/doing 习惯干某事
　　be used to do 被用来干某事
　　57. ◎useless
　　be ~to do / be ~ doing sth
　　He knew it was ~ to protest
　　It's ~ worrying about it.
　　use n.
　　1) make use of …
　　2 )be of great use to sb / be of no use to sb
　　3) It is no use doing sth
　　58. usual  a. 通常的  as usual 向往常一样

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