For years, scientists have believed that a certain hormone produced by the human liver was triggered by Enzyme U, which is released in the pancreas. Recently, however, researchers in Belgium discovered that Enzyme U is always preceded by the release of Enzyme W in the brain, and hypothesized that Enzyme W, not Enzyme U, triggers the release of the liver hormone. If a second research project were set up to verify the findings of the Belgian researchers, which of the following test results would most seriously weaken their hypothesis?

(5) The Belgian Researchers' CONCLUSION: Enzyme W, rather than U, triggers the release of the liver hormone.THE EVIDENCE: Enzyme U is always preceded by the release of Enzyme W. It's a classic causality question. Remember the key issues. We want to weaken a causal claim - that Enzyme W releases the liver hormone - so we ask whether the cause always precedes the effect (it should) or whether another cause could be at work (it shouldn't). If we get test results that present the liver hormone and Enzyme U's release, but not the release of Enzyme W, we have the effect (the liver hormone) without the cause (Enzyme W). We also have a strong case for another cause (Enzyme U). These test results hammer the researchers' conclusion. An example of the effect without the cause destroys a causal claim-some other cause must account for the effect.