[Dog Training] Nia and Bruno Enter into a Written Contract

Multiple Choice

[Dog Training] Nia and Bruno enter into a written contract for Bruno to train Nia's dog. Under the contract, Nia is required to pay Bruno $20 for each training session.
-What type of contract is the dog training contract?

A) Bilateral and express.
B) Bilateral and implied.
C) Unilateral and express.
D) Unilateral and implied.
E) Bilateral and unenforceable.