阅读下面短文，在空白处填入1个适当的单词或括号内单词的正确形式。
The polar bear is found in the Arctic Circle and some big land masses as
far south as Newfoundland. While they are rare north of 88°, there is evidence {#blank#}1{#/blank#}
they range all the way across the Arctic, and as far south as James Bay in
Canada. It is difficult to figure out a global population of polar bears as
much of the range has been {#blank#}2{#/blank#} (poor) studied; however, biologists
calculate that there are about 20,000-25,000 polar bears worldwide.
Modern methods {#blank#}3{#/blank#} tracking polar bear populations have been
employed only since the mid-1980s, and are expensive {#blank#}4{#/blank#} (perform)
consistently over a large area. In recent years some Inuit people in Nunavut {#blank#}5{#/blank#}
(report) increases in bear sightings around human settlements, leading to a {#blank#}6{#/blank#}
(believe) that populations are increasing. Scientists have responded by {#blank#}7{#/blank#}
(note) that hungry bears may be congregating (聚集)
around human settlements, leading to the illusion (错觉)
that populations are {#blank#}8{#/blank#} (high) than they actually are. Of {#blank#}9{#/blank#}
nineteen recognized polar bear subpopulations, three are declining, six {#blank#}10{#/blank#}
(be) stable, one is increasing, and nine lack enough data.
