Answer:
Because
Step-by-step explanation:
In the beginning of the sentence it states what happened, James was late to class and after that it states why, he didn't set his alarm clock the night before. When it comes to the options, before is in the sentence to describe when he was suppose to set his alarm. James was late to class, and he didn't set his alarm clock are just parts of the sentence. Because is set between the too parts of the sentence transition between what happened and why.