The simple past (also called past simple, past indefinite) is a verb tense which is used to show that a completed action took place at a specific time in the past. The simple past is also frequently used to talk about past habits and generalizations. The simple past is formed using the verb + ed. Questions and negative forms in statements are made with did and did not. Many verbs, such as "have," take irregular forms in the simple past. The verb "be" is also irregular in the simple past. Unlike other irregular verbs, there are two simple past forms: "was" and "were.
Since, we are talking about an action which has happened in the past, we will be using simple past tense. The verb in this case is "Be", so the simple past form is "was"
Option B is correct