A

Explanation:

If a contract cannot be performed due to the default of a third party on whom the promisor relied, the contract is generally not discharged unless the third party’s performance was a condition of the contract. The promisor remains liable for non-performance, as they bear the risk of the third party’s default unless otherwise stipulated. Option A (is not discharged) is correct. Option B (is discharged) is incorrect, as the promisor’s obligation persists. Option C (void) and D (voidable) are incorrect, as the contract remains valid but unperformed. The answer “A” aligns with contract law principles.