2013年4月gre考试备考：gre阅读考前热身试题（二十一）

Certain extremely harmful bacteria found only in sewage are difficult to detect directly. Testing for E. coli, an easily detected and less harmful type of bacteria, in ocean water would be a reliable way of determining whether or not these more harmful bac-teria are present, since ocean water contains E. Coli only if the water is contaminated with sewage that contains the harmful bacteria.

Which of the following, if true, most seriously weakens the argument?

(A) There are many different strains of the E. coli bacteria, and only some of these strains are harmful.

(B) Some types of bacteria found in sewage are neither disease-causing nor difficult to detect directly.

(C) Some of the types of bacteria found in sewage along with E. coli are not harmful to people unless the bacteria are ingested in large quantities.

(D) E. coli dies out much more quickly than some of the more harmful bacteria found in sewage and then can no longer be easily detected.

(E) Some of the types of bacteria found in sewage along with E. coli reproduce at a slower rate than E. coli.

答案：D