The correct option is D oral
Option A is incorrect because 'one' refers to a singular noun, whereas 'instructions' is a plural noun. Option B is incorrect because 'word' is a noun here and cannot modify another noun. Option C is incorrect because it's a part of speech, which refers to an action and wouldn't fit in the given context. Option D is correct because 'oral' means 'something that is spoken', and the instructions here are spoken.