这题我也选D,其实如果选A的话,unlike 就把Blassingame's study 与studies of earlier works on slavery 区分开,而根据A的意思,Blassingame的研究也是对earlier works (records)on slavery 的研究,本身包含在studies of earlier works on slavery中,自相矛盾了。
就好像说,Unlike Chinese cities, Shanghai is more westernized.
而D中是把earlier works on slavery 与Blassingame's study 比较,两者在时间上不相容、不重叠,可以比较。