Although ice particles in the upper atmosphere benefit Earth in that they reflect and absorb solar radiation, act as a global thermostat and thus keep Earth from either burning up or freezing over, while also accelerating the destruction of the ozone layer by reacting with chlorofluorocarbons (CFC's).
语法 Sentence Correction-3763
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图法法图a 2016-12-05 13:33:08
1.考点，句子结构，平行 2.看while后句子结构不完整
无敌的肥非仔 2015-10-14 11:46:00
act and keep在语法上作they的并列谓语，although与while都是引导状语从句，没有主句。
欧哦哦 2015-05-09 22:01:48
although为让步状语从句，不能单独存在，必须有一个主句，但是主句中缺少主语，故错误
JulianLoveGmat 2014-07-25 23:12:48
act...and keep 做之前从句中they的并列谓语， 故此选项无主句
