Several situations lend themselves particularly well to mixed methods $($MM$)$ research. Which situation is not one of them?

Group of answer choices

A formal structured instrument is desired, but first, the concepts need to be better understood

The qualitative results are puzzling, and quantitative results will help to explain them

An intervention needs to be developed with in$-$depth input from stakeholders, and then a rigorous, formal evaluation will be needed

The problem is complex, and neither a quantitative nor a qualitative approach is adequate by itself