Explanation:

- Symptomatic: This refers to something that serves as a symptom or sign, especially of a disease or condition. It is characteristic of or indicative of a specific condition.

- Optimistic: This means hopeful and confident about the future. It’s usually related to a positive outlook rather than being a sign of a condition.

- Characteristic: This means typical of a particular person, place, or thing. It often refers to something that reveals distinctive qualities, similar to a symptom revealing a condition.

- Correct Answer

- Strange: This means unusual or surprising in a way that is unsettling. It's not directly related to being indicative of a condition.

- Atypical: This means not representative of a type, group, or class. It’s more about being different than about indicating a condition.