Answer:
a. external
Step-by-step explanation:
External attributions are to explains situations or contexts, that are "out of our control", and that are supposed to explain why we behaved the way we did. It's an external reason than ourselves.
You arrive late home, past your curfew, you blame the party (external) that ended later than expected instead of saying "Yes, I should have left before the end of the party to be here on time" (internal).