The students stand on a pier（碼頭） over the Harlem River in New York City.They stare down into the brown water.Their teacher，Mr.Rodman，pulls a long rope out of the river.Fastened to the end of the rope is a metal cage and inside are oysters（牡蠣）.Taking turns，the students measure all the oysters，and then compare notes.The biggest oyster is over 2 inches long，much bigger than a healthy size for its age!They also measure the level of oxygen.As more oysters grow，the water should become clearer and hold more oxygen.Also，other animals should move in.
   Oysters are soft-bodied animals，and share the underwater community with plants，fish，and other life.They are food for crabs and other animals.As new oysters grow，they attach their shells to older ones，forming big reefs with many small spaces where other animals live.Oysters eat algae（藻類）.If algae grow too fast，they can decrease oxygen from the water-and even fish need oxygen to breathe!But what happened to the oysters 100 years ago in New York Harbor？Before then，lots of oysters lived in these waters.They were shipped to restaurants around the world.By the early 1900s.jye.ai were eating them faster than they could grow.Pollution was pouring into the waters.The harbor became seriously polluted.Since the 1970s，new laws have helped reduce poisonous waste.Some fish started to swim through again.But oysters were still missing-until recently.
   The Billion Oyster Project began in 2014 to help bring oysters back to New York Harbor.The project has recruited（招募） more than 6，500 students at more than 100 middle schools and high schools to help grow，distribute，and study the oysters.
   Finally，the students put the oysters back in the cage.Mr.Rodman lowers the cage into the river.In a few months，they will check the cage again.When the oysters are big enough，they will be moved to join a healthy reef in the middle of the harbor.

（1）Why do students come to the pier over the Harlem River？

A

A

A．To do research.
B．To go fishing.
C．To buy oysters.
D．To clean up the river.
（2）What is the second paragraph mainly about？

D

D

A．What oysters are like.
B．How oysters get fed.
C．Why algae grow fast.
D．What role oysters play.
（3）What can we learn about oysters in New York Harbor？

C

C

A．People's love of eating oysters boosted their numbers.
B．More oysters than before lived in waters in the 1900s.
C．Polluted water was partly to blame for the missing of oysters.
D．New laws in the 1970s were crucial to oysters 'recovery.
（4）Which of the following can be the best title for the text？

C

C

A．Oysters Raised in New York Harbor
B．The Harlem River Polluted Heavily
C．Nature's Helpful Crew Brought Back
D．Teacher Devoted to Wildlife Protection