听力原文： OK, in the last class we talked about the classification of trees and we ended up with-a basic description of angiosperm. You remember that those are plants with true flowers and seeds that develop into fruits. The common broadleaf trees we have on campus fall into this category. But our pines don't. Now ! hope you all followed my advice and wore comfortable shoes because as I said today we are going to do a little field study. To get started let me describe a couple of broadleaf trees we have in front of us. I'm sure you've all noticed that this big tree next to Brett Hall. It's a black walnut that must be 80 feet tall. As a matter of fact there is a plaque identifying. It is the tallest black walnut in the state. And from here we can see the beautiful archway of trees at the commons. They are American elms. The ones along the commons were planted when the college was founded 120 years ago. They have distinctive dark green leaves that look lopsided because the two sides of the leaf are unequal. I want you to notice the elm right outside the Jackson Hall. Some of the leaves have withered and turned yellow, maybe due to Dutch elm disease. Only a few branches seem affective so far but if this tree is sick it'll have to be cut down. Well, let's move on and I'll describe what we see as we go. What are the students going to do during this class period?