The correct option is B either ; or
Correlative conjunctions are pairs of conjunctions that work together. Some examples are either/or, neither/nor, and not only/but also. The given sentence requires the use of a correlative conjunction. The combination either/or indicates that there is a choice between the two choices, and only one can be selected. Either is always used with or and it is used to express alternatives and or a choice between two (and sometimes more) things. Thus Option B is correct. Besides, it is mentioned in the sentence that only one form is allowed. The combination neither/nor indicates that neither of the two choices can be selected. In other words, neither choice is available. Thus Option A is incorrect as neither/nor - When they're paired up they negate both parts of a statement while it is inferred in the sentence that one form is allowed. The combination both/and indicates that the two items are equally presented and included. Hence Option C is incorrect as it is inferred in the sentence that one form is allowed. We use' also' in the front position to emphasise what follows or to add a new point or topic. Since only one form is allowed Option D can be ruled out.