Ivan was interested in buying a $40$ acre parcel of commercially zoned property offered for Co$.$ He thought he might build a professional office complex, but would not know for sure until he consulted with soil engineers and architects. To make certain that the property was not taken off the market or sold to another buyer while he was deciding, he gave Land Co$.$ $$15,000$ to keep the offer open for $3$ months. This is an example of a

a$.$ Merchant's firm offer

b$.$ Option contract

c$.$ Preliminary negotiation

d$.$ Bargained for exchange