听力原文

Before we begin today’s experiment, let’s review the lab rules. First, safety glasses must be worn at all times, even if you’re only watching. Second, never mix chemicals unless the instructions tell you to do so. Today we’re using a strong acid which can cause serious burns if it touches your skin. If any chemical container is knocked over, DON'T PANIC! Tell me immediately and I’ll handle the cleanup. Also, keep your hair tied back and avoid wearing loose clothes. We will work in pairs. One person will handle the tools while the other records the data. Switch roles after every three trials to ensure everyone gets practice. Remember: the goal is accurate data, not speed. If you finish early, do not start a new experiment. Instead, clean your workspace thoroughly. Any questions? No? All right. Let’s have a safe and productive class.