Explanation:

- Ambiguous means unclear or open to more than one interpretation. It's often used when something is vague or not clearly defined.

- Annoying refers to something that causes irritation or discomfort. It doesn't directly relate to ambiguity.

- Stylish describes something fashionable or elegant. It’s not directly related to the concept of clarity or ambiguity.

- Sensational means causing great public interest or excitement. It's not an antonym of ambiguous, as it doesn't deal with clarity.

- Certain means definite, clear, and without doubt. It is the opposite of ambiguous as it implies clarity and being free from uncertainty.

Your answer is option 4- Certain.