THE usually means that we both know what we are talking about.
- I'm going to the post office to send these letters. (we know which one, the one the speaker usually goes to)
- Excuse me, is there a post office near here? (any post office, not a particular one)
- I don't drink tea. (any tea - I'm not talking about some specific situation and specific cup of tea)
- Did you drink the tea that I made? (we know which tea the speaker is talking about)
- I didn't like the film. (we know which film - the one that the speaker has just seen)
- Let's go and see a film. (the speaker doesn't say which one)
- Sam has two children, a boy and a girl. The boy is 5 and the girl 10. (mentioned for the second time - when we mention something for the first time, we are introducing it to the speaker, when we mention it for the second time, the speaker knows what / who we are talking about)
- Who is the girl over there. (we say which and where / not any girl, that girl over there)
- I think that I left the keys in the kitchen. (it's obvious which kitchen - it's clear from the situation)
- People used to think the Earth was flat. (there is only one)
- I'm the tallest girl in my school. (superlatives - because there is only one the tallest, best, fastest, etc)
- Bill, I'd like you to meet Robert De Niro, the actor (well known)
Exercises:
#1, Road to Grammar#2, Road to Grammar
#3, English Help
#4, British Council (easy)
#5, British Council (teens)
#6, Oxford University Practice
