A commonplace in genetics is the relationship between recombination frequency and crossover value. Generally speaking, ______.

A．recombination frequency may be directly obtained according to phenotypic ratios, but crossover value cannot be directly obtained according to phenotypic ratios
B．crossover value may be replaced by recombination frequency or chiasm frequency you get from the observation under microscope when genetic distance is considerably short
C．crossover value may be replaced by recombination frequency when genetic distance is as a medium value, not too long and not too short
D．recombination frequency will be very different from crossover value when there is a third locus in between the two loci you analysed

当前中国教育人类学的主要研究取向不包括（）。

A.弱势人群教育问题研究

B.有色人种教育问题研究

C.主流文化教育研究范型

D.少数民族教育研究模式