One Key to Effectively Using Prior Marketing Research Projects as Secondary

One key to effectively using prior marketing research projects as secondary data sources is

A) selecting only those projects that addressed the current problem.
B) using only project results that were generated by laboratory experiments.
C) always using project results in isolation,in other words,not confusing the issue by combining results from various projects.
D) combining key learnings on related topics in order to arrive at synergistic learnings.
E) using only the learnings from projects conducted by commercial research companies,in order to avoid internal bias.