单词拼写。
根据下列各句句意和空白之后的汉语提示词，在横线上写出对应单词的正确形式，每空只写一词。
1. We all know that he is too ________ (顽固) to apologize.
2. When the boiler ________ (爆炸) many people were hurt by the steam.
3. The scientists have made a ________ (有价值的) discovery recently.
4. More than 10,000 ________ (运动员) took part in the 29th Olympic Games in Beijing in 2008.
5. He ________ (承认) having killed his wife. So he was sentenced to death.
6. Many people are going to serve as ________ (志愿者) in the Guangzhou Asian Games.
7. What he's bought for me is ________ (正是) what I have been looking forward to.
8. In most maths examinations senior high school students are allowed to use ________ (计算器)
in the exams.
9. My uncle is grateful to me for________ (说服) him into giving up smoking.
10. At first, I thought these flowers were real, but they are ________ (人造的).