Sid contracts to put new kitchen cabinets in Ned's house. Sid repeatedly tries to install the cabinets, but Ned does not grant him access to the house. In this case:

$$ a$.$ the frustration of purpose doctrine applies to discharge the contract.

b$.$ Sid is discharged from his duties under the contract because Ned's prevention of Sid's performance constitutes a material breach.

c$.$ Ned is discharged from his duties under the contract because of material breach.

d$.$ Both Sid and Ned are discharged from their duties because of impossibility of performance.