We have to admit that the biggest___________ facing the ecosystem is limited resources and the worsening environmentA.missionB.challengeC.scaleD.contribution
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B解析试题分析：考查名词辨析A任务B挑战C刻度D贡献 题意为 我们不得不承认面对生态最大的挑战是有限的资源与糟糕的环境。在admit 的宾语从句中 the biggest changllege 是句子的主语，谓语是is ,表语是 limited resources and the worsening environment，分析清句子结构，很容易能得出