The passage is C. Studies...show that some people have fewer capsaicin receptors. They can usually handle eating more chiles than other people can.
How does the passage show the meaning ?
This passage directly explains how people experience chiles differently due to scientific factors. It states that some people have fewer capsaicin receptors, the receptors that detect capsaicin, the compound that makes chili peppers hot.
People with fewer capsaicin receptors are less sensitive to capsaicin and can therefore handle eating more chiles than people with more capsaicin receptors.