With no explanation, chose the best option from "A", "B", "C" or "D". on this point are not disputed by appellants. As the district court stated: In determining when and whether to mark a public work such as the sill in question, the United States considers, among other things: the degree of danger an object poses, the vessel traffic type and density, the location of the object in relation to the navigable channel, the history of vessel accidents, and the feasibility and economics, including costs, of erecting and maintaining physical markers in light of the available resources .... These are policy factors which require weighing competing interests to decide a course of action. These guidelines, leave room for and indeed require, the exercise of policy judgment based upon the resources available and the relative risks to the public health (5th Cir.1986) (<HOLDING>). C. Negligence of Hamilton The district

A: holding that decision to establish recreational swimming area was discretionary but failure to replace buoy secured by an anchor that injured a swimmer was not within discretionary function exception
B: holding that corps decision not to remove submerged unmarked piling was within discretionary function exception
C: holding that the discretionary function exception may apply in the absence of a conscious decision 
D: recognizing a discretionary function exception to that waiver
B.