a hearing aid的用法和样例：
- A hearing aid helps to overcome defects in hearing.
- A hearing aid helps most people to hear better.
- Grandmother's hearing is getting worse. She needs a hearing aid.
- My grandmother is hard of hearing and needs to wear a hearing aid.
- Grandmother' s hearing is getting worse. She needs a hearing aid.
- She is deaf in her left ear, even with a hearing aid.
a hearing aid的相关资料：
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