The correct answer is: “Were you in England in 1999?” “Yes, I was.”
The verb “to be” is conjugated in the past tense in this sentence because it is asking about a past event. The past tense of “to be” is “was” for singular subjects and “were” for plural subjects. In this case, the subject is “you,” which is a singular pronoun, so the correct verb form is “was.”
The other options are incorrect because they are not conjugated in the past tense. The verb “to could” is used to talk about ability or possibility, and the verb “to are” is used to talk about the present tense. The verb “to am” is the first person singular form of the verb “to be,” but it is not used in this sentence because the subject is “you,” which is a second person pronoun.