Here are the completed sentences with *there* or *it*:
1. **There's** another flight at 10.15. **It's** a Lufthansa flight.
*Explanation:* *There's* introduces the existence of another flight. *It's* refers to the specific flight being a Lufthansa flight.
2. 'Is **there** a gift shop?' 'Yes, madam. **It**'s on the first floor.'
*Explanation:* *There* introduces the existence of a gift shop. *It* refers to the specific location of the gift shop.
3. **It**'s too late, **there**'s nobody at the office.
*Explanation:* *It's* refers to the time being too late. *There's* introduces the absence of people at the office.
4. I know the Astoria. **It**'s an excellent hotel and **it**'s very near the airport.
*Explanation:* *It's* refers to the Astoria and its qualities (excellent hotel, near the airport).
5. **There**'s Internet access in each room and **it**'s free.
*Explanation:* *There's* introduces the existence of Internet access. *It's* refers to the fact that the Internet access is free.
6. Podgorica? I know **it**'s the capital of Montenegro, but what kind of place is **there**? Is **there** anywhere to go in the evening?
*Explanation:* *It's* refers to Podgorica being the capital of Montenegro. *There* introduces the question of what kind of place it is and the possibility of places to go in the evening.