Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that best combines each pair of sentences in the following questions.
All possible means have been used to prevent air pollution. The sky is still not clear.
A.Every possible means has been used to prevent air pollution so that the sky can be clearer.
B.The sky is still not clear due to the fact that all possible means have been used to prevent air pollution.
C.To prevent air pollution, every possible means has been used, and so the sky is still not clear.
D.Every possible means has been used to prevent air pollution, yet the sky is still not clear.

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