Researchers in City X recently discovered low levels of several pharmaceutical drugs in public drinking water supplies. However, the researchers argued that the drugs in the water were not a significant public health hazard. They pointed out that the drug levels were so low that they could only be detected with the most recent technology, which suggested that the drugs may have already been present in the drinking water for decades, even though they have never had any discernible health effects.

Reasoning of the Scientists - The drugs would have already been present in the water for decades and they have never had any discernible health effects.

Which of the following, if true, would most strengthen the researchers' reasoning?

A. If a drug found in drinking water is not a significant public health hazard, then its presence in the water will not have any discernible health effects. - This statement doesn't strengthen the point of scientists that the drugs were present for decades in the water.

B. There is no need to remove low levels of pharmaceutical drugs from public drinking water unless they present a significant public health hazard. - Not related to reasoning.
C. Even if a substance in drinking water is a public health hazard, scientists may not have discerned which adverse health effects, if any, it has caused. - This weakens the reasoning.

D. Researchers using older, less sensitive technology detected the same drugs several decades ago in the public drinking water of a neighboring town but could find no discernible health effects. - This is strengthening the reasoning clearly.

E. Samples of City X's drinking water taken decades ago were tested with today's most recent technology, and none of the pharmaceutical drugs were found. - This weakens the reasoning

In all the Strengthen questions, if we can find what we have to strengthen, the answer finding becomes very easy.