1.he has a toothache.

- toothache : đau răng

- a pain in tooth :một cơn đau ở răng 

2. what's the matter with your mother?

- what's the matter with sb?

 = what's wrong with sb

3. my brother often walks to school.

- walk = go on foot

5. he shouldn't ride his bike too fast.

- had better not = shouldn't ( shouldn't)

6. he has an earache

7.she has a stomach ache

Answer:

1. He has a toothache

`-` S + have/has + N + O

2. What's the matter with your mother?

`-` What's the matter with + S?

3. My brother often walk to school

`-` go on foot = walk

5. He shouldn't ride his bike too fast

`-` had better not = shouldn't

`-` shouldn't + V-inf

6. He has an earache

`-` S + have/has + N + O

7. She has a stomach-ache

6. He has an earache

`-` S + have/has + N + O