Conditional: If it dog scratches at the back door, then the dog needs to go outside. Converse: If the dog needs to go outside, then the dog scratches at the back door.

Which of the following biconditional statements can be written from the given statements?

A. The dog scratched at the door to go outside.

B. The dog needs to go outside, so the dog scratches at the back door.

C. The dog scratches at the back door, if the dog needs to go outside.

D. The dog scratches at the back door if and only if the dog needs to go outside.