Martial artists are capable of tolerating higher levels of pain than

Martial artists are capable of tolerating higher levels of pain than an average human being. Researchers studied the blood samples of Chung Lee – a renowned martial artist – and found more than average level of endorphins – certain biological compounds that can lower the perception of pain. Based on these findings, they concluded that the higher level of endorphins is the reason for the higher pain threshold in martial artists.

Which of the following, if true, helps assess the validity of the researchers’ conclusion?

A. Chung Lee can tolerate as much pain as every other martial artist.
B. The average of level of endorphins in people who practice martial arts is higher than the corresponding levels in other people in the world.
C. Endorphin levels are correlated with physical activity levels.
D. Endorphin levels tend to decrease with increasing sedentary lifestyle.
E. An older martial artist has lower endorphin levels than a younger one does.