You should stay home from school when you are sick.
Marty has to take a test at school but has flu symptoms.
Marty wants to take the test.
Marty calls his teacher and explains he is sick and arranges to take the test at a later time.
Marty goes to school and takes the test.
Marty is able to get over the flu and not risk the other students getting sick.
Marty gets the rest of his class sick with the flu.