Answer:
C, contingency
Step-by-step explanation:
A contingency contract is one in which a contract is based on conditions that requires certain actions for specific result/outcome. The contract can be called a if-then contract also. This means that if a party involved in the contract takes a particular action, the other party of the contract will also take an action that becomes an outcome.
From the above question, if the Ahmed family can close sale on their own home, then they can buy the Miller's home.
In the event that the Ahmed family does not fulfill the condition of closing the sale on their home, the Millers might not close the sale of their home to the Ahmed family as the contract is not binding on any of them.
Cheers.