The core concept is understanding the present perfect tense. The present perfect tense connects a past action to the present. Option D correctly uses the present perfect to indicate an action completed in the past that has relevance to the present. Option A uses the past simple ('visited') with 'yesterday', which is inappropriate for the present perfect. Option B uses the present perfect but 'just now' is more commonly used with the simple past tense, and Option C uses the future perfect tense, not the present perfect. The correct answer is D because 'have seen' correctly expresses an action completed in the past with relevance to the present. The word 'already' is often used with the present perfect tense.