题目内容：
请根据短文的内容，回答题。 Don't Rely on Plankton to Save the Planet
Encouraging plankton growth in the ocean has been touted by some as a promising way to remove carbon dioxide from the atmosphere. __________ (46)
Adding iron to patches of ocean can make plankton bloom temporarily. The microscopic organisms suck up dissolved carbon dioxide from the water, which in turn is replaced by carbon dioxide from the air. __________ (47)
Jorge Sarmiento from Princeton and his colleagues developed a complex computer model to analyze how factors such as ocean chemistry and water circulation would affect the process if 160,000square kilometers of ocean were seeded with iron for a month. __________ (48)
In their scenario, which covers an area 10 times as big as the largest experiment of this kind ever proposed, fertilizing the ocean removes 1 million tons of carbon from the atmosphere -- just 0.2 per cent of the carbon dioxide humankind spews out each month.
Rough estimates in the past have predicted similarly disappointing results. __________ (49) says Sallie Chisholm, an environmental engineer from the Massachusetts Institute of Technology.
"But the take-home message is the same. __________ (50)"
第46题___________ A．Its opponents argue, however, that it will stop global warming.
B．Its opponents fear that it will damage the marine ecosystem, and now a computer model shows that the trick would also be remarkably inefficient.
C．As plankton die and settle on the ocean floor, their carbon is supposedly locked up in the seabed.
D．They found that 100 years later only between 2 and 11 per cent, of the extra carbon that was originally taken up by plankton had actually been removed from the atmosphere.
E．"These are newer and better models."
F．Ocean fertilisation is not the answer to global warming.
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