GMAT Sentence Correction (SC) | Re: According to anthropologists, early religious beliefs were probably no

Here is a wrong comparison between an 'extant' or linking verb 'were' with an action verb 'began' in C and E. In the same vein, "were to have begun, in D and 'likely to begin' in D and A also denote an attempted action. In addition, A has the subject verb problem. All the four are out.
B is the reminder and we are force to select it more by chance than by choice. Because B as I see has a parallelism issue in not sticking to the tenets of correlative parallelism. "Not… but"
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