Which of the following statements is true? Select one: a. The GDP deflator compares prices in the current year with those in a reference year b. Real GDP is expressed in base-year dollars c. Nominal GDP is expressed in current dollars d. All of the above

Which of the following statements is true? Select one: O a. The GDP deflator compares prices in the current year with those in a reference year O b. Real GDP is expressed in base-year dollars O c. Nominal GDP is expressed in current dollars O d. All of the above