用所给数词的适当形式完成句子。
1. Today we'll study the _____ (9) lesson.
2. Jeff has _____(3) Chinese friends.
3. The Greens live on the _____ (5) floor.
4. This is Room _____(12). Your room is next to it.
5. February is the _____(2) month of the year.
6. Lesson _____(5) is very easy.