Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.
Not until Kentucky’s Mammoth Cave had been completely explored in 1972 _________.
A. when was its full extent realized
B. the realization of its full extent
C. was its full extent realized
D. that its full extent was realized
Answer the question before viewing the answer below
Correct answer: C