1 . The huge Florida wetland known as the Everglades is a slow﹣moving river 80 kilometers wide but only a few centimeters deep. People call the Everglades a "river of grass" because sawgrass covers most of it. Sawgrass is not really grass. It is a plant that has leaves edged with tiny sharp teeth that can easily cut through clothes ﹣and skin!

Travel in the Everglades is difficult. You cannot walk through shallow water because the sawgrass will cut you. The water is too shallow for regular boats. So， we use an airboat. An airboat is a flat， open boat. Like an airplane， it has a big propeller to move it. The propeller is fixed on the rear of the boat. It makes a loud noise but it does the job. The boat skims along the water's surface. Although we can still get lost in an airboat， at least we are above the alligators （短吻鳄）.

For a long time， dangers have threatened the Everglades. Around 1900， some people felt this precious wetland should be drained（排干）. They said it was just a big swamp and not good for anything. In the 1920s， there was a land boom in Florida. People wanted to build homes everywhere， including in the Everglades. They built canals， levees， and other water systems that stopped the rivers flowing into the Everglades. Factories were built near rivers that flowed into the wetland. These factories poured poisonous waste that damaged the environment of the everglades.

People are now working to preserve the Everglades National Park for the future. Right now one big problem is the paperbark tree. This tree is an invader from Australia.

Paperbark trees soak up a lot of water. In the early 1900s，people brought them to Florida because they thought they would help drain the Everglades. However， the invaders adapted too well. Paperbark trees have taken over hundreds of thousands of acres of the everglades and killed other trees. Scientists are cutting down these trees or spraying them with herbicides to kill them.

1. What possibly cause（s） airboats to get lost in the Everglades？

A．The sawgrass.

B．The vast river.

C．The alligators.

D．The shallow water.

2. Why do airboats take the place of normal boats？

A．Because they can move faster.

B．Because their noise frightens the alligators.

C．Because they have flat bottoms.

D．Because they carry more passengers.

3. How did people try to drain the Everglades？

A．By cutting down trees

B．By building factories.

C．By growing sawgrass.

D．By digging water channels.

4. Which category does the underlined word "herbicides" in the last paragraph belong to？

A．Seeds.

B．Poisons.

C．Crops.

D．Paints.