Sarah offers to pay Allison $150 if Allison will paint her apartment while she is out of town on vacation for two weeks. Allison makes no promise but tells Sarah that she will think about it. While Sarah is out of town, Allison paints the apartment. This is best described as___

Unilateral contract

Explanation:

Unilateral contract is a type of agreement or contract in which offer is made and fulfilled through performance .An offeror offers any promise to be fulfilled by him/her if the other party completes the performance act successfully.

According to the question,situation is described as unilateral contract as Sarah is offering $150 to Allison for painting her house in exchange.Allison has to complete house painting to gain promised money even though there is no legal contract between them.  

the right answer is a

answer; decipher the motives for why people behave the way they do;