An oil company conducted an investigation of the environmental effects

An oil company conducted an investigation of the environmental effects of oil spills and concluded that waterfowl exposed to oil spills have a 95 percent survival rate. The investigation, based on the examination of waterfowl admitted to a veterinary clinic near the site of a recent oil spill, noted that only one in twenty affected waterfowl died.

Which of the following, if true, would cast the most serious doubt on the investigation's conclusion about the survival rate of the waterfowl?

(A) Many of the affected waterfowl that survived the spill had suffered serious injuries.
(B) Each affected waterfowl that died was larger than average for its species.
(C) Most of the affected waterfowl were exposed to oil floating on the surface of the water.
(D) Very few of the affected waterfowl were readmitted to the clinic after reexposure to the oil.
(E) Only those affected waterfowl that appeared to stand a good chance of survival were brought to the veterinary clinic.