c. construct validity

    Correct.

Construct validity refers to the degree to which inferences can
legitimately be made from the operationalizations in your study to the
theoretical constructs on which those operationalizations were based.
For example, if you only use a single version of a self-esteem measure, you
can't provide much evidence that you're really measuring self-esteem. Your
critics are likely to argue that you aren't measuring self-esteem but are
only measuring part of it. Solution: try to implement multiple measures of
the key construct (e.g., self-esteem) and see if you get similar effects in
your studies.