trt    y
   a 18.2
   b 18.6
   c 22.8
   d 17.7
   a 19.5
   b 21.6
   c 22.0
   d 17.0
   a 22.2
   b 23.1
   c 22.9
   d 18.6
   a 26.8
   b 27.5
   c 21.4
   d 16.6