#1.  3 pts

     1 pt  make-singles (map)
     2 pts merge-all-neighbors (generative recursion)

#2.  3 pts

     There's different ways to break this up into helper functions.
     Grading should put more emphasis on the generative recursion that
     on the math details.

#3.  4 pts

     2 pts integrate-dc with rectangles
     1 pt  integrate-dc with trapezoids
               should be organized to only change one helper function
     1 pt  integrate-adaptive
               should be organized to only change the termination condition

As usual, also remember the standard guidelines about templates, tests, etc.