The correct option is D either ; or
A conjunction combines or connects two sentences as one. They can be a word or a phrase (like even if, as well as, etc). Correlative conjunctions are words in pairs that connect two sentences, but they're not written together, for example, either...or, but...and, such...that, etc. In the given sentence, the speaker offers the listener something, and gives him a choice, to "take it" or "leave it", so a pair of correlative conjunctions is required that refers to choice. 'Either...or' is used in a sentence in the affirmative sense, when referring to a choice between two possibilities, and is suitable for the given sentence, hence option B is correct. 'Neither...nor' is the negative equivalent to 'either...or', it means 'not either', and is used when none of the possibilities are chosen. It cannot be used here, as the first sentence "This is all I can offer right now" means the speaker is offering something, and it's left to the person to take it or leave it. The speaker can't say 'you can neither take it nor leave it' which contradicts the first statement, hence option D is incorrect. 'Either' is always paired with 'or', as both are in the affirmative, and 'neither' with nor', as both are negative, 'either' can't be paired with 'nor' and 'neither' with 'or'. Also, 'nor' is not used where 'neither' is also not used, hence options A and C are incorrect.