a medical certificate的用法和样例：
- Can I have a medical certificate?
- A medical certificate issued by a registered practitioner.
- Such illness must be attested to by a medical certificate.
- Absentees should ask their parents to notify the school of their absence. They should submit a parents' letter and a medical certificate to the form teachers as soon as possible.
- On appeal, the airman argued that the bipolar disorder diagnosis was "invalid" and, thus, should not disqualify him from receiving a medical certificate.