Final answer:
The reminder about Josephine's dentist appointment on the refrigerator is a simple sentence.
Step-by-step explanation:
The question is asking whether the reminder about Josephine's dentist appointment on the refrigerator is simple, complex, or neither. In this case, the reminder is a simple sentence because it consists of a single independent clause: 'Josephine found a reminder about her dentist appointment on the refrigerator.' There aren't any extra phrases or dependent clauses that complicate the sentence.