Suppose the total market value of all the final goods and services produced in the country of Rushya was $8 billion in 2018 (measured in 2018 prices) and $9 billion in 2019 (measured in 2019 prices). Which of the following statements is definitely correct?
a. Production increased in Rushya between 2018 and 2019
b. Real GDP increased in Rushya between 2018 and 2019
c. Average price levels increased in Rushya between 2018 and 2019
d. Whether real GDP increased cannot be determined with the information given