根据括号中的汉语提示，在空白处用单词的正确形式完成句子。
1. She stood up ______ (突然) and went out of the room.
2. America ______ (发现) by Columbus.
3. I have read the book which ______ (介绍) China in detail.
4. He ______ (醒来) early yesterday morning.
5. The old man decided to ______ (比较) this picture with that one in order to find some differences.
6. I have been there ______ (几十) of times.
