If Nominal Gross Domestic Product (GDP) in 2001 Was $1

If nominal Gross Domestic Product (GDP) in 2001 was $1 trillion, nominal Gross Domestic Product (GDP) in 2013 was $2 trillion, and the 2001 and 2013 price indexes were 100 and 250 respectively,

A) real Gross Domestic Product (GDP) increased between 2001 and 2013.
B) real Gross Domestic Product (GDP) decreased between 2001 and 2013.
C) real Gross Domestic Product (GDP) remained constant.
D) we cannot draw any conclusions about changes in real Gross Domestic Product (GDP) .