Simplify the following text for a Grade 8 native English-speaking person.
Original: The Professor talks with Peter and Susan ; he does not understand why they do not believe Lucy 's story and gives them three possible explanations of Lucy 's behavior â '' madness , dishonesty and sincerity â '' the others know she is neither mad nor dishonest , so she must be telling the truth .
Simplified: The Professor talks with Peter and Susan , and he tells them that Lucy 's story might be telling the truth .