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。
Thevolunteerswouldrathergobytrainthan________.
Linguistscanconcentrateonalltheaspectsoflanguageatonce.
Lyingundertheskull,thehumanbraincontainsanaverageoftenbillionnervecellscalled______.
Alinguistictheoryisconstructedaboutwhat______isandhowitworks.
Thesyntacticrulesofanylanguageare______innumber.
