【正确答案】The rock formations in caverns are made up of water that's saturated with dissolved minerals. As they drip and deposit themselves in the cave, you'll notice some of them hang from the ceiling and some of them grow up from the floor. The terms for each of these deposits are so similar that the professor suggests some tricks to help keep them straight. Stalactite has the letter t in it, which reminds students of a tail that hangs down...but stalagmite has the letter m in it, which brings to mind two points that stick up. He also points out that stalactite has a c in it, like the word ceiling, and stalactites drip down from the ceiling, but stalagmite has a g in it, like the word ground, and stalagmites grow up from the ground. So...so these, uh, memory aids...they help us recall that stalactites are the rock formations that grow down from the cavern and stalagmites are the ones that grow up from the floor.

【答案解析】[听力原文] Okay, as you'll recall, caves form in limestone when acidic groundwater follows some kind of weakness in the rocks. Now the rock formations in a cavern...that's the technical name that we use for a cave...the rock formations there are of two kinds...stalactites and stalagmites. Both of these formations are water that contains dissolved minerals that...that accumulate and build deposits. But stalactites hang down from the ceiling of the cavern, and stalagmites protrude up from the floor of the cavern. Well, these words sound a lot alike, and this can be confusing, so I always tell my students to remember that there is a t in stalactites, and the t has a tail that hangs down just like the stalactites that hang down from the ceiling of the cave, but there is an m in stalagmites and the points on an m stick up like the stalagmites that protrude up from the ground in a cave. And if that doesn't work for you, another way to remember the difference is that stalactite has a c in it, and so does the word ceiling, whereas stalagmite has a g in it, and so does the word ground. So stalactites drip down from the ceiling and stalagmites build up from the ground. So with these little tricks for remembering the difference, I expect you all to get this right on the next quiz.