According to the Bank of Canada's website, Canada's Consumer Price Index (CPI) in August 2012 was 121.8, August 2013 was 123.1, August 2014 was 125.7 and August 2015 was 127.3. Given this set of index numbers, what can we conclude about average prices in Canada between August 2012 and August 2015?

average prices decreased each year

average prices decreased over this time period by 5.5%

average prices increased each year

average prices increased over this time period by 5.5%

average prices increased over this time period by 27.3%