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。
Researchfindingshaveshownthatlanguageprocessingcentersaresituatedinasingleareaofthelefthemisphere.
Childrenhaveanatural________abouttheworldaroundthem.
Weather_______,we’llgooutforawalk.
Youngerchildrenarecurious________howthingswork，andmanyofthemwanttotakeaparteverythingwithintheirreach.
Ifpaymentisnotreceived,legalactionwillbeouronly________.
