Client $C$ is in a very competitive category with equal market share of the top three brands. The client is convinced that it has changed every marketing$-$mix variable possible except for package design. Since the three competitive brands are typically displayed side$-$by$-$side, Client C wants us to determine what factors of package design $($e$.$g$.,$ size, shape, color, texture$)$ cause an increase in awareness, preference for, and intention to buy the brand. What do you recommend for the appropriate research design?

Secondary data

Descriptive research

Exploratory research

Causal research

Longitudinal study