听力原文：M: Have you done the lab for physiology yet -- the one on taste? W: Yeah, it was kind of fun -- mapping the taste buds. Didn't you think so? M: I'm doing it this afternoon. How long will it take? W: It went pretty quickly -- under an hour, anyway. See first you mix up the four solutions. M: You take water and add either sugar, lemon juice, salt, or -- oh -- What was it? W: Bitter quinine. M: That’s it -- oh -- then what? W: Then all you have to do is taste each sample and describe where each flavor seems most intense. M: Is that hard? W: Not really. One thing to remember though -- not all the taste buds are on the tongue. M: Right. I’ll keep that in mind. And thanks for going over this with me. Maybe we could talk about this after I' ve tried it -- we could get a pizza or something. W: Great. Give me a call. What is the main purpose of the lab experiment?