用下列各词的适当形式填空。

1. The children were __________ because they didn't get Christmas presents. (happy)

2. You must always hide __________ from children. (medical)

3. December is the __________ month of the year. (twelve)

4. The doctor's __________ made all of them sad.(dead)

5. I think this dictionary is __________ for your study. (help)

6. Which river is the second __________ river in the world? (long)

7. It is a __________ for me to stay with you. (please)

8. They don't know why you talked to them so __________. (angry)

9. Someday you'll find a foreign language a bridge to a lot of __________. (know)

10. Who is the book __________ (write) by?