Theunderlinedsentenceinthelastparagraphprobablymeansthat______.
A.theproblemisnotapproachedstepbystep
B.theresearchessofarhavefaultsinthemselves
C.theproblemistoodifficultforresearcherstodetect
D.researchinthisareaisnotenoughtomakegeneralizedpatterns
正确答案:D


