11.at the end of 在…的结束时，在…末尾
We are given an examination at the end of each month.
我们每个月底都有一场考试。
12.be keen on 喜欢，热爱，醉心于…
I am keen on studying English.
我热心于学习英语。
13.next to 挨着，在...旁边
Who’s the boy sitting next to you?
坐在你边上的那个男孩是谁?
14.in the middle of 在…中间
Don't put the sand in the middle of the path!
别把沙子倒在路中央。
15.work as 担任，从事
I will study science well and work as a scientist.
我要学好科学，将来做个科学家。
16.be responsible for 为…负责
He was responsible for making plans for the meeting.
他负责做会议计划。
17.pay(...)for 为…付钱，赔偿
We have to pay 345 yuan for the cost of the trip.
我们必须为这次旅行交345元。
18.for free 免费地，无偿地
The website provides English vocabulary to everyone for free.
这个网站免费向每一个人提供英语词汇。
19.try one’s best 竭尽所能;尽力，尽自己最大努力
Students ought to try their best to learn all subjects well.
学生应该尽力学好每一门功课。
20.believe in 信任
We do not believe in God.
我们不相信上帝。