SFX Paintball Games Inc., and Truck & Trailer Delivery Corporation sign an agreement that provides for the payment of "$1,000 by whichever party commits a material breach of the contract that creates damages difficult to estimate but approximately $1,000 by whichever party commits a material breach of the contract that creates damages difficult to estimate but approximately $1,000." This is .
a. A liquidated damages clause
b. A mitigation of damages clause
c. A nominal damages clause
d. A penalty clause