1.（2019全国I卷）Modem methods of tracking polar bear populations have been employed only since the mid-1980s, and are expensive ______ (perform) consistently over a large area.
【答案】to perform
【解析】考查非谓语动词。主系表结构之后，常用不定式作原因或目的状语，句意：跟踪北极熊的现代方法只是在二十世纪八十年代以来开始采用，并且在如此大区域内持续采用是昂贵的，故此处用to perform。
2.（2019全国I卷）Scientists have responded by _____ (note) that hungry bears may be congregating(聚集) around human settlements, leading to the illusion(错觉) that populations are higher than they actually are.
【答案】noting
【解析】考查非谓语动词。根据其前介词by可知，此处用动名词主动形式，故填noting。
3.（2019全国II卷）A 90-year-old has been awarded “Woman Of The Year” for ______ (be)Britain's oldest full-time employee-still working 40 hours a week.
【答案】being
【解析】考查非谓语动词。根据其前介词for可知，此处用动名词形式作宾语，故填being。
