Answer:
B. Hansel or Gretel.
Step-by-step explanation:
Hansel signed a contract with Shade Tree Landscaping so he can enforce the contract, i.e. sue Shade Tree if they do not perform their part. But Gretel, as a third party beneficiary, can also sue Shade Tree for breach of contract. In contract law, a third party beneficiary can sue the breaching party even if it was not part of the contract but the breach of the contract generates some type of suffering to them.
In this case, Gretel was not part of the contract, but because Shade Tree is not performing, she will be hurt by it.