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根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。 Tired of traditional running? Well, maybe it's time to try using your hands instead. That's what Shaun McCarty and other Australians are doing — running on all fours. McCarthy, who comes from Melbourne, Australia, said he's the one behind the term “crunning.” “It's not crawling, it's not running.” he said. “Crunning is a better workout than running. It puts more of an emphasis（着重）on the body than traditional running does. ” McCarthy thinks that he 下列有关生物变异的说法，不正确的是 A．一对父本和母本通过有性生殖产生的后代，个体之间总会存在一些差异，这种变异主要来自基因突变 B．镰刀型细胞贫血症属于可遗传的变异 C．基因重组能够产生多种基因型 D．非同源染色体之间相互交换片断属于染色体结构变异