o(∩_∩)oOnly when the whole city was covered in the thick fog _______ the importance of environmental protection.A.people realized B.people had realized C.did people realize D.had people realized 请问一下为什么这题应该选择C而不是D

o(∩_∩)oOnly when the whole city was covered in the thick fog _______ the importance of environmental protection.A.people realized B.people had realized C.did people realize D.had people realized 请问一下为什么这题应该选择C而不是D
o(∩_∩)o
Only when the whole city was covered in the thick fog _______ the importance of environmental protection.
A.people realized
B.people had realized
C.did people realize
D.had people realized
请问一下为什么这题应该选择C而不是D呢?

o(∩_∩)oOnly when the whole city was covered in the thick fog _______ the importance of environmental protection.A.people realized B.people had realized C.did people realize D.had people realized 请问一下为什么这题应该选择C而不是D
同学,很高兴回答你的问题
正确答案确实选C
即：Only when the whole city was covered in the thick fog did people realize the importance of environmental protection.
翻译：只有当整个城市笼罩在浓雾之下,人们才会意识到环保的重要性.
解析：only 在句首时句子要倒装,句子为主从复合句,则主句倒装,从句不倒装.本句中从句的时态是一般过去时,那么主句的时态也要用一般过去时,不能用过去完成时,因为when 的意思是当...时,一般前后的时态应该是一致的,如果主句的动作发生在从句的动作之前,则主句用过去完成时,即“过去的过去”.而本句主句的动作应该是发生在从句的动作之后的,即先浓雾笼罩城市,后来人们才意思到,显然不能用过去完成时,所以D是错误的.
再给你看一道类似的例题,
Only when _____ home_____ that he had left his bag in the taxi he had taken.[ ]
A.he returned; did he realize
B.did he return; did he realize
C.he returned; he realized
D.did he return; he realized
Only when _____ home_____ that he had left his bag in the taxi he had taken.
A.he returned; did he realize
B.did he return; did he realize
C.he returned; he realized
D.did he return; he realized
答案：A
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D only when 提前句子要倒装

C.only 开头部分倒装，即用助动词/情态动词放于句首
前面是过去时所以用did 倒装
D选项是过去完成时强调动作发生在whole city was covered 前与题意不符排除

此为Only的倒装句 the whole city was covered in the thick fog被提前，而前句有was，如果为正常语序应为people did realize，但因倒装，故选C

因为出现了only在句首，所以要倒装
然后从句中是was，一般过去时，主句用had 的话是发生在过去的过去，也就是was covered 之前，与句意不符。

题中有was，说明是过去时，而realize并非发生在cover之前，故用一般过去式，选C

C 1）语序问题：only +状语（可能是副词、介词词组或是状语从句） 放在句首，句子需要用部分倒装（若有从句的话，注意是主句倒装）； 2）时态问题：“只有当整个城市被笼罩在浓雾之下的时候，人们才意识到环保的重要性”was covered 与realiezed 都应用过去式。...

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C 1）语序问题：only +状语（可能是副词、介词词组或是状语从句） 放在句首，句子需要用部分倒装（若有从句的话，注意是主句倒装）； 2）时态问题：“只有当整个城市被笼罩在浓雾之下的时候，人们才意识到环保的重要性”was covered 与realiezed 都应用过去式。

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