A survey result shows that cell phone usage among teenagers rose from 63% in 2006 to 71% in 2008. Of the following choices, which statement about cell phone use among teenagers is true?
a. Cell phone usage rose by 11.2 percentage points.
b. Cell phone usage rose by 12.7 percentage points.
c. Cell phone usage rose by 12.7%.
d. Cell phone usage rose by 8%.