Which of the Following Formulas Should Be Used to Calculate $\frac { \text { CPI } 2010 - \text { CPI } 2009 } { \text { CPI } 2010 } \times 100$

Which of the following formulas should be used to calculate the inflation rate between 2010 and 2009?

A) $\frac { \text { CPI } 2010 - \text { CPI } 2009 } { \text { CPI } 2010 } \times 100$
B) $\frac { \text { CPI } 2010 } { \text { CPI 2010-CPI 2009 } } \times 100$
C) $\frac { \text { CPI } 2010 - \text { CPI } 2009 } { \text { CPI } 2009 } \times 100$
D) $\frac { \text { CPI } 2010 - \text { CPI } 2009 } { \text { CPI base period} } \times 100$