Thisisanimportantproblem_______toofewsocialscientistshaveresearched.
A、whichD
into which 引导的是 problem 的定语从句。 which 指代 problem ，into 与 research 搭配。
EmpiricalstudiesshowthattheprocessofSLAisaprocessofconstructingandmodifyingrulesofcommunication.
―________finedayitistoday!
Werefertothelimitedrangeofsoundsasthephonicmediumoflanguageandindividualsoundswithinthatrangeas______.
Johnsonwas________unknownbeforerunningforthepresidency.
Lyingundertheskull,thehumanbraincontainsanaverageoftenbillionnervecellscalled______.
