In each of the following situations will performance be discharged$/$ excused due to impossibility?

a$.$ Paul, a famous singer$,$ contracts to perform at your wedding. Paul dies prior to the wedding day.

b$.$ You have a contract to buy Sarah$$s house. Before the closing, Sarah dies.

c$.$ You have a contract to buy one thousand bushels of pears from Gro$-$Moore farms. Because of a hail storm, Gro$-$Moore is unable to deliver the pears.