Answer:
The correct answer is - C. The grandmother did not sign the letter containing her promise to guarantee the loan.
Explanation:
Suretyship is a three-party contract, that states that one party who is a guarantor normally promises the obligee or a second party that the surety will be responsible for any debt of a third party resulting from the principal's failure to pay as decided.
This contract must be signed by the party to be charged but in the given case grandmother had not signed the letter that has no written promise to act as a guarantee of the loan her friend give to her grandson, the Statute of Frauds would prevent enforcement of her promise.