Use one sentence to explain why GAAP needs conservatism principle to constraint the revenue recognition.

On January 1, Jack signed a contract with AT &T for his mobile phone services. The contract includes three lines with a $120 fixed payment each month plus $15 per gigabit if the data usage is more than 9 gigabits. On March 1, Jack wants to add one more phone line to the existed contract, and the payment becomes $150 fixed payment each month plus $15 per gigabit if the data usage is more than 12 gigabits. Is this change a contract modification? Please use one sentence to explain why?

Taylor Construction Inc. signed a contract with FSU to build a student residential building with two million dollars by 2021 August; FSU can only pay 1.8 million dollars if Taylor cannot complete the construction by September 1. According to the consideration of the four transaction price types, which type is for the following transaction