Preposition of medium/material – writing instrument and ink: choose the correct preposition used with ink. Sentence: "The answer was written ____ blue ink." Select the standard preposition that indicates medium.

Given data

• We need the preposition used to express the medium/material (ink) of writing.

Concept/Approach
English uses in to denote the medium or language: "written in ink/pencil/blue", "written in French". With names the instrument ("with a pen"), not the medium. By indicates agent; on indicates surface.

Option analysis
in — correct: "written in blue ink". ✅with — would be "with a blue pen", not "with blue ink".by — marks agency ("by John"); not used for medium.on — indicates surface ("on paper").

Final Answer
in