Reasonable Variable Ordering

Consider a scheduling problem, where there are five activities to be scheduled in four time slots. Suppose we represent the activities by the variables A, B, C, D, and E, where the domain of each variable is {1,2,3,4} and the constraints are A>D, D>E, C ≠A, C>E, C ≠D, B ≥ A, B≠C, and C≠D+1. [Before you start this, try to find the legal schedule(s) using your own intuition.]
Show how backtracking can be used to solve this problem. To do this, you should draw the search tree generated to find all answers. Indicate clearly the valid schedules. Make sure you choose a reasonable variable ordering.
To indicate the search tree, write it in text form with each branch on one line. For example, suppose we had variables X, Y, and Z with domains t, f and constraints X ≠Y and Y≠Z. The corresponding search tree can be written as:
X=t Y=t failure
Y=f Z=t solution
Z=f failure
X=f Y=t Z=t failure
Z=f solution
Y=f failure
(Use this book as a reference, everything explained here: http://artint.info/html/ArtInt_72.html)