30 Extensive tagging programs have been carried out； they nevertheless tell us little more than that the salmon is likely to be found anywhere within thousands of miles of its origins. (A) Thanks to extensive programs, we now know more about how the salmon survives far away from its origins. (B) Although plenty of research has been done, we still don’t know much about where to find salmon. (C) Extensive searching programs have been launched to study the salmon within thousands of miles of its origins. (D) Extensive tracking programs have done little in helping uncover salmon’s mysterious life.