Final answer:
The provided excerpts do not include information about Agatha or Professor Sader, so it is impossible to determine what Professor Sader told Agatha to do if she had questions.
Step-by-step explanation:
The content provided does not contain any direct information about what Professor Sader told Agatha to do if she had questions. All the excerpts seem unrelated to each other and do not mention a character named Agatha or Professor Sader. The excerpts appear to be from different stories or texts and deal with various situations and characters. Therefore, it is impossible to ascertain from the given information what Professor Sader advised Agatha to do regarding her questions.