the thick clouds, you would find the kite in the sky easily.
A. Had it not been for
B. If it were not
C. If it had not been for
D. Were it not for
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A. Had it not been for
B. If it were not
C. If it had not been for
(答案→)D. Were it not for
解析：句意：要不是因为厚厚的云层，你就会容易的发现天上的风筝。结合主句中的would do可知是和现在相反的虚拟语气，从句应该用if it were not for the thick clouds这时可以将if，were提前，所以选D。