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.
The snowfall was so heavy. All the trains were delayed.
A.Had it been for heavy snowfall, all the trains would have been delayed.
B.Only by a snowfall was heavy did all the trains were delayed.
C.So heavy was the snowfall that all the trains were delayed.
D.Not until all the trains were delayed was the snowfall heavy.