You can go neither by train ____ by bus.

The sentence “You can go neither by train ____ by bus” requires the correlative conjunction “nor” to pair with “neither” in a negative construction, indicating both options are unavailable. In English, “neither…nor” is used to negate two possibilities. Options A (or, used with either), C (and, affirmative), and D (but, contrastive) do not form the correct negative structure, making “nor” the appropriate choice for this sentence.