Passage Summary: Researchers gave a group of rats lots of salt and found that most of them ended up with high blood pressure, leading them to conclude the salt was the cause.

Conclusion: There is a causal or correlative link between high-salt diets and high blood pressure in rats.

Reasoning: In a study where a colony of rats was fed a high-salt diet, 75 percent of the rats developed high or extremely high blood pressure after a few months.

Analysis: To evaluate this argument, we need to know if the high blood pressure was actually caused by the salt or if it's just a normal trait of this rat colony. Without a control group—rats fed a normal diet—we don't have a baseline for comparison. If 75 percent of rats in this colony develop high blood pressure regardless of what they eat, the study's results are meaningless. Look for an answer choice that asks about the blood pressure levels of rats not fed the high-salt diet.