Which of the Following Statements Is True

Which of the following statements is true?

A) Only one model is needed to fully understand the workings of the macroeconomy.
B) Generally, macroeconomic models do not require assumptions because they are based on mathematics.
C) Different macroeconomic models focus on the relationships between different variables or on different problems.
D) Economics has largely abandoned model building since advances in information technology have made current macroeconomic data widely available.