if you change all the fractions to a common denominator then it will be easier to compare fractions. in this case the greatest common denominator is 60. you can find the the greatest common denominator by finding the greatest common factor of the numbers
5/6 = 50/60
11/20 = 33/60
-9/10 = -54/60
by doing this we can see that 5/6 is the closest fraction to 1. if you are confused on the -9/10 that is the closest to -1 not 1.