1.（2019全国I卷）Of the nineteen recognized polar bear subpopulations, three are declining, six _____ (be) stable, one is increasing, and nine lack enough data.
【答案】are
【解析】考查主谓一致。根据three are declining，此处数词six作主语，代指前文中的“polar bear subpopulations”，故用复数谓语，一般现在时，故填are。
2.（2018全国I卷）While running regularly can't make you live forever，the review says it ，cycling or swimming. (be) more effective at lengthening life than walking
【答案】is
【解析】考查时态和主谓一致。本文介绍了跑步的好处，通篇以一般现在时为主。本句中宾语从句与主句的时态应保持一致，故用一般现在时；且宾语从句中的主语为it，故用is。
3.（2017全国I卷）Fast food ( be) full of fat and salt；by eating more fast food people will get more salt and fat than they need in their diet.
【答案】is
【解析】考查时态和主谓一致。根据行文的时态可知，此处用一般现在时；句子的主语fast food(快餐)是不可数名词短语，故填be的第三人称单数形式is。
