People used to see lots of plastics on the sea surface.Now in a study，researchers have found that the microplastic pollution in deep water is much more serious than that on the sea surface."What we've known about microplastic has been from the sea surface，"says Kyle Van Houtan，"but this study suggests there's a larger amount that's unnoticed."
   Microplastics are small pieces that break from plastic bottles or bags as they change to simplerchemical forms in the environment.They have different sizes and can be found anywhere，including in the oceans，lakes，soil and even blowing in the air.
   To study microplastic pollution in deep sea，Houtan's team collected samples（样本） in the sea by using a ROV（遥控潜水器）.As the ROV went down from 5 to 1，000 meters below the sea surface，a specially-designed machine filtered（过滤） the sample water and kept the small particles（微粒）.Back in the lab，the team used a special machine to find out the types of plastic present.
   Although the researchers found microplastic was everywhere，the amount of the particles was not evenly spread in the water.The midwater，180 to 460 meters below the surface，held the highest amount of microplastic pollution，about four times as much as on the surface.Van Houtan thinks this may be because when plastic breaks down into ever-smaller pieces，they are covered with biological material，which causes them to go down into the deep-sea area.
   Their findings are based only on a certain area，and if the results hold for the wider ocean environment，the amount of plastic in the midwater would be worrying，because this is key living environment for most sea animals.These particles，which have harmful chemicals，can go into the food webs at both the ocean's surface and seafloor，and can influence reproduction of sea animals.The final effect remains unknown，but what is for certain，Houtan says，is that"this is a serious problem，and it shows humans can change natural systems."
   Yet in other ways，"the results are encouraging，"he says.Since most of the microplastic waste comes from single-use plastic，this means we could reduce microplastic pollution by cutting down on the production and use of the unnecessary plastic products.

（1）Houtan's team used ROV to

B

B

.
A．filter the sample water
B．collect samples in the sea
C．examine the chemicals
D．record the depth of water
（2）What can we learn from the study mentioned in the passage？

C

C

A．The sea surface is the most seriously polluted.
B．Deep-sea animals will die out in the near future.
C．The midwater holds the most microplastic particles.
D．Biological material destroys the food webs in deep sea.
（3）What is the writer's main purpose in writing this passage？

A

A

A．To remind people to reduce plastic waste.
B．To explain causes of microplastic pollution.
C．To introduce changes in the ocean ecosystem.
D．To advise people to recycle single-use products.