Professor Lilli Gans wishes to study the relationship between people's zodiac sign and their political opinions. She asks the students filling out her questionnaire to put their names on the front so she can ask for clarification or elaboration of some answers later. However, she promises that no one other than she will find out who gave what answer. Professor Gans is promising:

$$ both anonymous and confidential.

anonymous but not necessarily confidential.

confidential but not necessarily anonymous.

neither anonymous nor confidential.