1. General question:
Did I meet them at the airport yesterday?
Was St.Petersburg founded in 1703?
2. Wh-question:
Whom did I meet at the airport yesterday?
Where did I meet them yesterday?
When did I meet them at the airport?
When was St.Petersburg founded?
3. Tag question:
I met them at the airport yesterday, didn't I?
St.Petersburg was founded in 1703, wasn't it?
4. Alternative question:
Did I meet them at the airport or at the bus station yesterday?
Was St.Petersburg founded in 1703 or in 1715?
5. Subject question:
Who met them at the airport yesterday?
What city was founded in 1703?