In a recent experiment, researchers concluded that the phenomenon known as runner' s high was caused by a biochemical reaction in the brain. Long-distance runners who ran long enough produced chemicals that have an opioid-like effect on mood. These runners not only felt euphoric after running, but they had a higher pain tolerance than the average person as well. Which one of the following is most strongly supported by the information above? ["The average person will not experience feelings of euphoria unless they have runner's high.", 'The feeling of euphoria is almost always caused by the act of running.', "Those who have runner's high will experience euphoria as well as a higher pain tolerance.", 'Long-distance runners have a higher pain tolerance than the average person.']