Which of the following would be an example of openings Pandora's box?

a. A school decides to give out next year's class lists before summer break, and now everyone is complaining about what friends aren't in their classes.

b. A teacher gets her Scholastic book box, but one of the books she ordered is missing.

c. A student forgets to study for the spelling test and misses 12 of the 20 words.

d. A principal organizes a field day for the students, but then has to cancel because of rain.