This is an important problem _______ too few social scientists have researched.
A、whichD
intowhich引导的是problem的定语从句。which指代problem，into与research搭配。
Linguistscanconcentrateonalltheaspectsoflanguageatonce.
Theconclusionfromthestudyisnotdefinite;itisjust________.
Thisisanimportantproblem_______toofewsocialscientistshaveresearched.
Johnsonwas________unknownbeforerunningforthepresidency.
Hetalkedalotaboutthingsandpersons________theyrememberedintheschool.
