I really am not understanding what they are saying regarding a permutation being necessary.... Can you steer me in the right direction on this word problem?

A social scientist conducts a study with 10 subjects. In which situations is a permutation necessary to determine the number of possible outcomes?

Administer a survey to 6 of the subjects.

Invite 3 subjects to participate in a repeat study.

Make a seating chart for the 10 subjects around a table.

Schedule interviews for all 10 subjects.

Select 3 out of 6 sandwiches and 2 out of 4 desserts for the subjects' lunches.