Choice "C" is correct. Owen will be liable for 50% of the loan balance. The release of one co-surety (Ward) without the consent of the other co-surety (Owen) discharges the remaining co-surety's (Owen) right of contribution from the released co-surety (Ward) and discharges the remaining co-surety to the extent the released party was liable. Owen and Ward were equally liable on the debt. Thus, Ward's release will release Owen from 50% of Owen's liability.
Choice "b" is incorrect. A release of a surety does not affect the liability of the principal debtor. Thus, because Lark is the principal debtor, the release of Ward (the surety) does not affect Lark's liability.
Choices "d" and "a" are incorrect. The release of one co-surety without the consent of the other co-surety discharges the remaining co-surety to the extent the released party was liable. Ward was equally liable on the debt with Owen. Thus, the release of Ward releases Owen from liability for half of the loan balance.