大学英语：build up (建立;增强;增加)

　　They worked hard to build up the friendship between the people in two countries.

　　Get plenty of exercise every to build up your health.

　　2. come across (穿过，出现;遇到)

　　They came across the street to meet me.

　　A good idea came across my mind

　　We are bound to come across difficulties， but we are determined to overcome them.

　　3. look up (查阅)

　　If there are words you don't understand， look them up in the dictionary .

　　For further information about this matter， look up this book.

　　4. at top speed (以最高速度)

　　He drove his car at top speed

　　It's dangerous to corner at top speed