阅读下列短文，根据短文内容填空。在未给提示词的空白处仅填写1个适当的单词，在给出提示词的空白处用括号内所给词的正确形式填空。

    The goshawk, a rare bird, once close to extinction, has doubled  (it) number in a national park in the south of England. Around 100 years ago, there were thought to be no goshawks (leave), due to farmers hunting them and their woodland habitats being cut down. However, thanks to conservationists, goshawks are back. By monitoring their nesting sites over time, the teams have been able to protect them from further forestry work. As a result, their number (grow) from just 20 pairs to 40 pairs in the past two years.