1. i'm sorry. you missed katie. she left the office about three minutes ago!

just
yet
already

2. you've finished your dinner ! you must have been starving!

yet
already
just

3. i've seen your teacher, and he's told me that you haven't finished your assignments

just/yet
just/already
already/yet

4. you phoned at the right time. i've finished my homework!

already
just
yet

5. they haven’t seen st. paul’s cathedral

already
yet
just