Which sentence has an unnecessary comma?

a) a week prior, all of the couples made plans to go out to dinner before the night of the big dance.
b) the principal of our high school, declared that everyone must show their student id at the door.
c) our high school parking has too few spaces, and it doesn't have a convenient entry way.
d) when the family had its monthly meeting, the parents presented a plan to buy a kayak.