Here, there is an important word, which is THEIR, in non-underlined part. THEIR is used for what? Is it used for ANCESTORS or THE TRIBES?
Actually, ‘THEIR’ is used instead of THE TRIBEs not ANCESTORs, because the location of ANCESTORS is INSIDE of preposition/ prepositional phrase (OF the…). When we have something INSIDE of preposition, then it can’t be subject for a single moment! So, we need a subject in the underlined part. But, in option C and D, the location of the subject (THE TRIBES) is also INSIDE of preposition/prepositional phrase (OF the…). But, we are NOT allowed to use subject THE TRIBES inside of preposition. So, we must cross out option C and D in case of above discussion.
In option A, ‘THEY’ is used for what? In this option, ‘THEY’ is trying to indicate “a well structured traditional society’’. But, is it possible to use THEY as a pronoun of “a well structured traditional society’’? ---Nope. We are not permitted to use ‘THEY’ instead of SOCIETY! So, option A is cross out as well.
In option E, “well structured” is the modifier of “traditional Society”. So, we should not separate it by THAT clause. Also, “a traditional society that is well structured” makes weird sound. The use of “a well structured traditional society” is perfectly fine. Because, the tribes of South Africa have a “well structured traditional society” NOT the tribes of South Africa have a “traditional society that is well structured”’ which is weird to hear! Most importantly, THAT clause did not complete the sentence; so, it is sentence fragment.
In option B, the intended meaning of the sentence and grammar structure have been used perfectly. So, the correct answer is choice B.
Thanks to all…