Which of the following statements is true?

a$.$The new standard, Revenue from Contracts with Customers, recognizes revenue based on a revenue$-$expense approach.

b$.$The converged standard on revenue recognition entitled Revenue from Contracts with Customers was developed because$$GAAP had only one basic standard on revenue recognition before.

c$.$the current revenue recognition principle recognizes revenue when it is earned.

d$.$A key feature of revenue recognition is that the signing of the contract by the two parties is not recorded $($does not result in a journal entry$)$ until one or both of the parties perform under the contract.