Logical subjects

Determine which of the highlighted designators are logical subjects of their sentences:

1. John believes the man in the brown hat is a spy.
2. The longest line on the London underground system used to be the Piccadilly line, but it is now the Central line.
3. The prize winner is by definition the person that wins the prize.
4. Hesperus was so-called because it was visible in the evening.
5. Hesperus is Phosphorus.