Answer:
The word in this sentence that you need to emphasize to best convey meaning is necessary.
Explanation:
By emphasizing the word necessary the message becomes utterly imperative and it shows the great importance of mathematics in the process of 3D character modeling, It makes it an impossible to substitute ability in the field, therefore this conveys the message the best way, clearly and correctly. The other words could give a sarcastic impression in the context by being emphasized.