Identify the principal clause in the following sentence.
Zyan, who is a postman, is my childhood friend.

A subject, an infinite verb, and an object comprise a principal clause. Option A is the correct choice among the options presented above because it makes complete sense without the rest of the sentence. It can exist on its own. It has a finite verb (is), a subject (Zyan), and an object (childhood friend). It is correct grammatically. This clause does not require the other clause (subordinate clause), namely "who is a postman." Option B is incorrect because it is the subordinate clause, contains the subordinate conjunction 'who,' and relies on the main clause or principal clause to make sense. It is either grammatically incorrect or makes no sense on its own.

Option C is incorrect because it contains elements from both the main and subordinate clauses. Option D is incorrect because the structure is incomplete; it does not make sense on its own, which violates the principal clause rule, which states that a structure can exist independently and be grammatically correct. As a result, b, c, and d are all eliminated.