重点讲解：
1. be supposed to do sth.
应当，应该，须做某事；
eg. She was supposed to be speaking about sales figures, but she kept wandering off the subject.
她本该谈论销售数字，但她老是跑题。
eg. You are not supposed to gull your friends.
你不应该欺骗你的朋友。
2. knock on
敲；击；
eg. Please do not enter before knocking on the door.
进来前请先敲门。
eg. He went up the garden path to knock on the door.
他穿过花园小径去敲门。
3. fly into
突然爆发（坏脾气）；突然陷入（恐慌）；
eg. Losing a game would cause him to fly into a rage.
输掉一场比赛会让他暴跳如雷。
eg. In fact, she was not a woman who would fly into a passion.
事实上，她不是那种动辄发火的人。