Answer:
a. interviews were expensive to conduct
Step-by-step explanation:
The disadvantage of in depth interview contained in the scenario is that face to face or in-depth interviews are expensive to conduct.
The rationale behind this conclusion is as presented in the scenario that ''In order for executives to agree to the interviews the company provides a large cash incentive.''
The fact that in-depth interview could be paid for, in order to guarantee its occurrence; is a practical display of the fact that in-depth interview or Face-to-Face method, is very expensive.