This time Expert Lecture 4 came to our classroom. Mr. Feng came in to talk to us about his job. He is a chemical engineer. He taught us about how to get rid of trash around the world. For example is was telling that we still don’t know what to do with our trash. We put our trash in machines that make it into balls or squares and other shapes, but we throw it into the ocean or burn it which bad for the environment.For example, when you burn the trash it is created into one of the three phases, gas, water and solid. In this case the burned trash turns into gas which pollutes the air. There is also something called super critical fluids that can decompose trash. In the older days people used a chemical that was in the coffee that causes cancer. But later people Used super critical fluids to extract the coffee from the beans. I thought this was was a fun and exiting visit!