Answer:
The answer is: C. Roland glanced over his shoulder — John was following him!
Step-by-step explanation:
Dashes are used to make a pause, they are different in usage to a hyphen as this last is used to separate words, not groups of words as dashes do. In this case, we can see that the sentece has "somehow finished": Roland glanced over his shoulder... we made a pause to add extra information which here is basically the reason for why he glanced over his shoulder. The other examples do not have a pause, for instance the first option is only a question which is not adding extra information not making a pause, as it's pretty linear. Option B doesn't have a dash before the one at the end, so this is incorrect. and finally letter D, as letter A, doesn't need a pause there, and it is not adding extra information, the extra information is given after the comma.