报道说，此前，北极熊和灰熊曾在动物园内被配对成功，而且它们还生下了后代。 北极熊和灰熊这两种不同种类的熊，其繁殖期大致相同，但相比较而言，北极熊的繁殖期要比灰熊来得稍稍早一些。
Stirling said polar bears and grizzlies have been successfully paired in zoos and that their offspring are fertile, but there had been no documented case in the wild.
不同种类的有孔虫在不同温度下繁殖。
Different types of foraminifera thrive at different temperatures.
某些种类的病毒使细胞迅速繁殖并产生癌。其它种类的病毒或者几种不同种类病毒的结合引起普通感冒。
Some kinds of viruses cause cells to multiply rapidly and produce cancer. Other kinds of viruses, or a combination of several different kinds, cause the common cold.
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