Scientists believe that either volcanic activity or large meteor impacts______wh

游客2025-06-12 13

问题 Scientists believe that either volcanic activity or large meteor impacts______what led to the extinction of the dinosaurs.

选项 A、is
B、has been
C、are being
D、are

答案 D

解析 that从句“that…dinosaurs”的谓语动词空缺，空格前的主语为either A or B(A或B中任一的)结构，动词应与B(large meteor impacts)保持单复数一致，故动词的复数形式(C)和(D)为备选答案。根据上下文语义，此处意为“火山活动或流星冲撞导致了恐龙的灭绝”，因此用于表示当前状态的一般现在时(D)are为正确答案。(C)are being为现在进行时，表示现在正在进行的动作，与上下文语义不符。作为参考，what从句“what…dinosaurs”是充当be动词are的补语的名词性从句。

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