The correct answer is: "social media has become an important tool in presidential campaigns".
The graph shows the number of related Tweets (measured in millons) that were published online during the 2009 and the 2012 presidential campaigns in the US. The figure has grown from 10 million Tweets in 2009, to over 30 million in 2012. If using this figure as a benchmark to measure the influence of social media, it can be claimed that it has grown a 200%.
