Mr$.$ Smith owns an apartment complex with extensive lawns and garden areas. He enters into an informal written contract with A$1$ Lawn Service to perform all of the lawn and garden work in his complex including mowing, weeding, and watering. Which of the following is true of this scenario?

a$.$ Either party can change the terms of the contract at any time.

b$.$ It is a legally binding contract.

c$.$ This contract must be oral, not written.

d$.$ No contract has been formed.