Questions 21～25 are based on the following passage． Supporters of the biotech industry have accused an American scientist of misconduct after she testified to the New Zealand government that a genetically modified （GM）bacterium could cause serious damage if released．
The New Zealand Life Sciences Network，an association of pro-GM scientists and organisations，says the view expressed by Elaine Ingham，a soil biologist at Oregon State University in Corvallis，was exaggerated and irresponsible． It has asked her university to discipline her．
But Ingham stands by her comments and says the complaints are an attempt to silence her． “They’re trying to cause trouble with my university and get me fired,”Ingham told New Scientist．
The controversy began on 1 February，when Ingham testified before New Zealand’s Royal Commission on Genetic Modification，which will determine how to regulate GM organisms． Ingham claimed that a GM version of a common soil bacterium could spread and destroy plants if released into the wild． Other researchers had previously modified the bacterium to produce alcohol from organic waste． But Ingham says that when she put it in soil with wheat plants，all of the plants died within a week．
“We would lose terrestrial （生的）plants．．．this is an organism that is potentially deadly to the continued survival of human beings，”she told the commission． She added that the U．S．Environmental Protection Agency （EPA．canceled its approval for field tests using the organism once she had told them about her research in 1999．
But last week the New Zealand Life Sciences Network accused Ingham of “presenting inaccurate，careless and exaggerated information”and “generating speculative doomsday scenarios （世界末日的局面）that are not scientifically supportable”． They say that her study doesn’t even show that the bacteria would survive in the wild，much less kill massive numbers of plants． What’s more，the network says that contrary to Ingham’s claims，the EPA was never asked to consider the organism for field trials．
The EPA has not commented on the dispute． But an e-mail to the network from Janet Anderson，director of the EPA’s bio-pesticides （生物杀虫剂）division，says “there is no record of a review and/or clearance to field test”the organism．
Ingham says EPA officials had told her that the organism was approved for field tests，but says she has few details． It’s also not clear whether the organism，first engineered by a German institute for biotechnology，is still in use．
Whether Ingham is right or wrong，her supporters say opponents are trying unfairly to silence her．
“I think her concerns should be taken seriously． She shouldn’t be harassed in this way,”says Ann Clarke，a plant biologist at the University of Guelph in Canada who also testified before the commission． “It’s an attempt to silence the opposition．”
第21题：The passage centers on the controversy （）．

A. between American and New Zealand biologists over genetic modification
B. as to whether the study of genetic modification should be continued
C. over the possible adverse effect of a GM bacterium on plants
D. about whether Elaine Ingham should be fired by her university