Which of the Following Would Be Considered an Example of the Drop-Off

Which of the following would be considered an example of the drop-off survey?

A) A researcher brings a questionnaire to a respondent's home and leaves it to be completed.
B) A hotel leaves a questionnaire in a room for customers to evaluate their accommodations.
C) A retail store offers a customer a survey and promises a gift certificate if they return the questionnaire on their next visit.
D) A graduate student hands surveys out to other students to be placed in a drop box when completed.
E) All of the above would be considered drop-off surveys.