What Does It Mean to Operationalize a Research Question

What does it mean to operationalize a research question?

A) Operationalizing is finding out how research subjects will behave under test conditions.
B) Operationalizing is testing the research question to find out if it will work.
C) Operationalizing is determining the operations and techniques to be used to assess a research question's key concepts.
D) Operationalizing is making agreements with publishers to produce copies of research study results.