69.

Answer and Explanation

Your Answer is

Correct Answer is B

Explanation

The underlined part is followed by an object clause: the final price of a human voyage to Mars would be. According to the meaning of the sentence "one can only imagine what the final cost of people landing on Mars" choose What, item B is correct.

Item C: how can also guide the object clause, but it means "way", which does not conform to the meaning of the sentence.