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阅读理解 Reintroducing beavers (海狸) to Britain could help clean up rivers,prevent flooding and minimise soil loss, an expert has claimed. Professor Richard Brazier, a researcher at the University ofExeter, said unpublished results from a trial area in Devon showed muddy water enteringan area where beavers were living was three times cleaner when it left. Ourtrial has shown that the beavers are able to dam our streams in a way that keepssoil in the headwaters of our catchment (流域) so it doesn't block up rivers downstreamand pollute our drinking and bathing waters. If we bring beaver具有两种相对性状的纯合体亲本杂交，子一代自交，若符合自由组合定律，则子二代个体中重组类型所占的比例为A．9/16 B．3/8 C．3/8或5/8 D．3/16或1/16