Here are the correct forms of the words along with explanations for each:

1. This tree has a lot of green **leaves**. (LEAF)
- Explanation: The word "leaf" in its plural form is "leaves," which refers to the many flat, green structures on trees.

2. I don’t like **sunny** weather. (SUN)
- Explanation: The adjective form of "sun" is "sunny," which describes weather that is bright and clear with a lot of sunlight.

3. Mai’s sister is a **singer**. (SING)
- Explanation: The noun form derived from "sing" is "singer," which refers to someone who sings, especially professionally.

4. His **teeth** are small and white. (TOOTH)
- Explanation: The plural form of "tooth" is "teeth," which refers to the hard structures in the mouth used for biting and chewing.

5. Lee is from China. She is **Chinese**. (CHINA)
- Explanation: The adjective form relating to China is "Chinese," which describes anything pertaining to China, including nationality.

Feel free to ask if you have any further questions!