Answer:
c .When they reached the summit of Haleakala, it was almost dawn, they took pictures of the sun risingover the volcanic rim.
Explanation:
As you can see, the phrase shown in the question aciam, presents a sequence of activities that a group of individuals performed on the summit of Haleakala. These activities must be separated by commas, however, as it is a sequence of activities, it is not correct that the last comma is accompanied by the word "and", which means that option A is incorrect.
It is also not correct to use the adverb "then" after the pronoun "they", which indicates that option B is also incorrect and option C is correct.
