Explanation:

- Cogent: This word typically means clear, logical, and convincing. It's often used to describe arguments or reasoning that are compelling and well-presented.

- Option 1, Rational: This means something that is based on or in accordance with reason or logic. Similar to cogent, it emphasizes clarity and logical strength.

- Option 2, Insane: This means in a state of mind which prevents normal perception, behavior, or social interaction. It’s the opposite of logical, so it's not synonymous with cogent.

- Option 3, Tyrannical: This indicates an oppressive or controlling manner, which is unrelated to being clear or convincing.

- Option 4, Coward: This is a term for someone who lacks courage. It doesn't relate to clarity or logic.

The most fitting synonym for "Cogent" is Rational.

Correct Answer: Option 1, Rational