Petor Is Trying to Be as Efficient (And Frugal) as Possible

Petor is trying to be as efficient (and frugal) as possible in designing the interviews that must be conducted as part of his experiment. Which of the following options are associated with reduced costs (an option that is unrelated to cost should not be circled) ? (choose all that apply)

A) structured interviews
B) unstructured interviews
C) open-ended questions
D) closed-ended questions