this is easy. all you have to do is find a common numeral between each number in each ratio. a ratio is in its simplest form when the two numbers have no numeral in common (for example A being 11:12). B and C both could be simplified because 4 and 28 can both be divided by 4 and 7 and 14 in answer C are both divisible by 7. answers D and E, however, are both already simplified like answer A.
