Off the coast of Formentera,an island,lives seagrass that stretches 15 kilometres.The seagrass,covering several hectares,is made up of a single organism.The grasses are also long-lived,for tens or hundreds of thousands of years.Along with two other kinds of coastal ecosystems—mangrove swamps and tidal marshes,seagrass meadows are particularly good at taking carbon dioxide from the air.
This role was highlighted in a report,which was published on March 2nd by UNESCO，on blue carbon—the carbon taken in by Earth's oceanic and coastal ecosystems.In total around 33 billion tons of carbon dioxide,about three-quarters of the world's emissions（排放）in 2019，are locked away in the planet's blue carbon sinks（碳汇）.Research by Carlos Duarte,the report's author and a marine ecologist,has shown that one hectare of seagrass can suck as much carbon dioxide each year as 15 hectares of rainforest.
One reason that blue-carbon ecosystems make such effective sinks is that underwater forests are thicker than the land-based woods.They can also trap floating pieces and organic matter,which settles on the sea floor and can double the amount of carbon stored away.They have another advantage,too.Climate change is leading to more wildfires around the world.As forests burn,their carbon stocks are released back into the atmosphere.Unlike forests on land,blue-carbon ecosystems do not burn.
Blue-carbon ecosystems may not be fired,but they remain affected to other sorts of disasters.In May 2020 hurricane Amphan destroyed 1，200 square kilometres of mangrove forest.A marine（海洋的）heatwave in Australian waters in 2010 and 2011 damaged around one third of the world's largest seagrass meadow in Shark Bay. "Mangrove forests can weaken or control waves and provide natural barriers to storm surges.Protecting and expanding them,then,appears to be a must," said a marine biologist.



What does the second paragraph mainly talk about？ ______

A. The real definition of blue carbon.
B. The special features of the seagrass.
C. The doubt about the blue-carbon ecosystems.
D. The capacity of the blue-carbon ecosystems to store carbon.

Why can the blue-carbon ecosystems make such effective sinks？ ______

A. They aren't influenced by natural disasters.
B. They have great ability to absorb carbon.
C. Their carbon stocks are released back.
D. There are more underwater animals.

What do the marine biologist's words mean？ ______

A. Humans should preserve blue-carbon ecosystems.
B. Mangrove forests can strengthen waves.
C. Mangrove forests are too strong to be broken.
D. Blue-carbon ecosystems can be fired.

What is the best title for the text？ ______

A. Blue-Carbon Ecosystem Are Expanding Much Faster
B. The Grasses Can Store More Carbon Than Your Expectation
C. Mangrove Forests Can Control Waves Efficiently
D. Plants in the Ocean Are Better at Storing Carbon