听力原文：PERRY: Hi, Opal. Any ideas about what we should do for our geography project？OPAL

听力原文：PERRY: Hi, Opal. Any ideas about what we should do for our geography project？

OPAL: Hi, Perry. Yes, I'd like to do something on Wetlands.

PERRY: I think that's a great idea—where do we start？

OPAL: With a definition of course—something like: ' a marshy area of land where the soil near the surface is saturated or covered with water, forming a special habitat for wildlife'.

PERRY: And we could add: 'the flora and fauna of the area are reliant on the water-logged soil for their survival'.

OPAL: Yes, that's a major problem actually—when commercial developers or farmers come along and decide to drain the swamps—everything dies. The practice is all too common unfortunately. Did you know that, as a result, wetlands are recognized internationally as one of the most threatened types of habitat？

PERRY: That's right. We'll have to be sure to discuss their importance in our assignment.

OPAL: But, first, I think we should state some of the particular characteristics of wetlands.

PERRY: Well, there are three that I can think of. To start with: wetlands are limited areas of open water, which vary depending on seasonal fluctuations.

OPAL: Yes...and the second could be that there's usually a variety of water-tolerant flora on the banks and throughout the water.

PERRY: Of course, depending on the time of year, there may be more or less water but levels generally remain quite shallow.

OPAL: Okay...now let's move on to the importance of wetlands.

PERRY: Shall we start with plant and wildlife habitat？

OPAL: Yes, I think we should point out that wetlands are homes for countless species of water birds, frogs, invertebrates and fish...

PERRY: ...and they support many varieties of water-loving plants...

OPAL: which brings us naturally to the topic of biodiversity—even small wetlands act as borders between land and permanent water. They turn into refuge areas or sanctuaries in times of drought and they often support rare and threatened plants and animals found nowhere else.

PERRY: Exactly. And they're especially important as nurseries and breeding grounds for all kinds of fish, birds and invertebrates.

OPAL: Wetlands are important for improving the purity of the water, too.

PERRY: Yes, that's because the flow of water through the wetlands is slowed by bank and in-stream plants, and so it allows sediment to settle. Nutrients, such as nitrogen and phosphorous and other pollutants are removed as the water passes through.

A wetland is an area where the soil is typically water-logged. Plants and animals living there depend on the we ness for their (21) Draining swamps is a widespread occurrence which kills off wildlife and, consequently, wetlands are (22) worldwide. It is a feature of wetlands that conditions vary according to (23) Water-tolerant plants grow both in and out of the water and water levels are usually (24) Wetlands naturally occur between land and water and become (25) for various wildlife during very dry periods. They also act as nurseries for different kinds of animal life. Wetlands are known to upgrade (26) by removing pollutants.

A．water quality

B．seasonal change

C．saturated soil

D．safe places

E．quite low

F．quite high

G．nutrients

H．nurseries

I．international recognition

J．farming activity

K．extinct

L．continued existence

M．commercial development

N．at risk

(15)