Example of a strong and weak entity types

Just to play with it, question is strong entity type and answer is weak. Question is always there, but an answer requires a question to exist.

Example: Don't ask 'Why?' if Your Dad's a Chemistry Professor

A weak entity is one that can only exist when owned by another one. For example: a ROOM can only exist in a BUILDING. On the other hand, a TIRE might be considered as a strong entity because it also can exist without being attached to a CAR.