Jenny,who Is 16 Years Old,pays $950 for a Diamond Necklace

Jenny,who is 16 years old,pays $950 for a diamond necklace from her local jewellery shop.Jenny's mother is horrified at the cost and takes Jenny back to the store to demand a refund.The owner refuses.As Jenny and her mother leave the shopping centre they see the same necklace on special at another jewellery shop for $600. Under common law,the likely legal position is:

A) Jenny was buying something which was for her benefit.She will be bound by the contract.
B) Jenny was not buying something which is a 'necessary'.She is not bound by the contract.
C) Jenny was not buying something with her mother's consent.The contract is voidable.
D) Jenny knew what she was doing and is bound by the contract.