This question is asking for the smallest difference between the max and the minimum. To get that, subtract the low from the high.
Atlanta:
106-(-12)=106+12=118
Boston:
103-(-19)=103+19=122
Chicago:
100-(-32)=100+32=132
Dallas:
111-(-8)=11+8=119
Since 118 degrees is the smallest difference, and that correlates with Atlanta, Atlanta is your answer.
Hope this helps!