What is the answer to the macroeconomics question?

8. Real GDP can be calculated using which of the following methods: (a) quantities produced in different years using prices from a year chosen as a reference period (b) quantities produced in different years with the prices that prevailed during the year in which output was produced (c) quantities of goods produced in consecutive years using prices in both years and averaging the percentage changes in the value of output (d) prices at different points in time using a sample of goods that is representative of goods purchased by households