1．They were both uncertain (无把握的) about what to do and went to their uncle for help.
2．If a student lacks (缺乏) the motivation to study, he will quickly become tired of studying.
3．Paper, iron and glass are all materials which can be recycled (回收利用) and used again.
4．Teachers think highly of Alice, because she is constantly (不断地) working hard.
5．My sister is optimistic (乐观的) about her chance of winning the English speech contest.
6．Cities are usually warmer than surrounding (周围的) rural areas, so it's wise to live in cities in winter.
7．You should make a good impression (印象) on somebody when you first meet.
8．All passengers on board are expected to fasten (系牢) the seat belts when the plane takes off and lands.
9．Mr.Brown is my previous (早先的) teacher, who taught me physics in my secondary school.
10．They have decided to make a few adjustments (调整) to their travelling plan.
