托福TPO72听力Lecture2原文+题目+答案+MP3音频下载

托福TPO72听力Lecture1原文+题目+答案+MP3音频下载

Listen to part of a lecture in a botany class.

Professor:

Ok. During the break, some of you have some questions. And while we were talking, I mentioned that my family owns a maple syrup business in the Massachusetts. And some of you asked, if I talk a little bit about how that works, give you a brief lesson in applied button as David put it. So, yes, ok. Well, maple sap is collected from several species of maple trees that grow primarily in the northeastern United States and southeastern Canada. You know you don't actually get syrup from a maple tree ready to put on your pancakes. What you get is sap that can be made into syrup. So first, sugar is created through photosynthesis, then it's converted into starch, and it's set for storage, usually in the roots of the tree.

Then as springtime approaches, the starch is converted back into sugar. The sugars and starch is dissolved in this watery liquid that we call sap. They're moved around to various places in the tree, in vessels that are referred to as phloem. So phloem can either move sugar down toward the roots or up toward the leaves, or horizontally from one side of the tree to another. During the spring in proper weather conditions, the sap in the tree begins to rise.

And for this sap to move throughout the tree, the weather conditions have to be just right, when the days become mild above freezing and the nights are still freezing. So there needs to be an alternate, warm day and below freezing night. We're still not totally sure exactly how this promotes sap ..........余下托福TPO72听力Lecture2原文省略！

(1)、(单选题) What does the professor mainly discuss?

A.The function of sap in maple trees

B.The process of maple sap production

C.The process of converting maple sap into maple syrup

D.The relationship between weather conditions and maple sap characteristics

(2)、(多选题) The professor makes the point that cells in maple trees are mostly filled with gas. What does this point explain

(Click on 2 answers)

A.How maple trees convert sugar to starch

B.What causes sap to move up the trunk of the maple tree

C.Why minerals easily dissolve in the sap of maple trees

D.Why sap flows out of maple trees when they are tapped

.........余下托福TPO72听力Lecture2题目省略！

完整版托福TPO72听力（C1+L1+L2+C2+L3）原文+题目+答案+MP3音频下载，15元有偿！