Step 1: Identify the clue.
“Group data based on similarity” and “no DV/IV distinction” point to interdependence methods (e.g., cluster analysis, factor analysis, multidimensional scaling).
Step 2: Eliminate distractors.
(b) Dependence requires a specified dependent variable.
(c) “Multivariate” is broad and includes both dependence and interdependence; the stem is specific.
(d) Univariate uses one variable at a time.
\[
\boxed{(a)}
\]