This is an important problem _______ too few social scientists have researched.
D
intowhich引导的是problem的定语从句。which指代problem，into与research搭配。
Childrenhaveanatural________abouttheworldaroundthem.
I was writing a report last night; ________ I would not have stayed up late.
Alinguistictheoryisconstructedaboutwhat______isandhowitworks.
______ofasentencedependsonthecontextinwhichthesentenceisuttered.