Final answer:
The correct answer is A. have just seen.
Step-by-step explanation:
The correct answer is A. have just seen.
In this conversation, Don asks John if he knows where Julia is. John responds by saying 'Yes, I have just seen her.' The correct form of the verb to use here is 'have just seen' because it is in the present perfect tense. The past simple form of the verb 'see' is 'saw', but the present perfect tense is formed by using the auxiliary verb 'have' followed by the past participle of the main verb.
Example: I have just seen the movie.