Conclusion: The choice of which projects to cancel was clearly motivated by party politics.
Premise 1: Most of the scheduled highway projects were in districts controlled by the President's party
Premise 2: Of those that have been canceled, nearly two-thirds were in districts controlled by opposition parties
Problem solving: As this is a strengthening question, we need to find an option that strengthen the author's argument.
A. The only uncanceled highway projects in districts controlled by opposition parties are those few that promise significant economic benefits to neighboring districts controlled by the President's party. -> I will keep (A), as it adds another reason to support the argument; uncanceled highway projects in districts controlled by opposition parties actually help those in districts controlled by President's party.
B. Virtually all the canceled highway projects involved the relatively inexpensive renovation of existing highways rather than the far more expensive construction of new highways. -> Whether renovation is expensive or inexpensive has nothing to do with the argument in this context.
C. One of the opposition parties controls no districts in which highway projects were originally scheduled. -> This is a confusing option IMO. I will leave (C).
D. Although the total cost of the canceled projects comprises a relatively small proportion of the government's total budget, it comprises a large proportion of the highway budget. -> Whether the projects take a large proportion of the highway budget has nothing to do with the author's argument.
E. No more than one highway project was canceled in any one legislative district. -> This information provides nothing to the argument.
Now we're down to (A) and (C). The option (C) is saying that "one" of the opposition parties and the fact that "one" opposition party controls no district in which highway projects were originally scheduled does not add much to the argument. So the answer will be (A).