Concept:The preposition "since" with a specific point in the past is used with the present perfect tense to show an action that started then and continues up to the present.
Explanation:The phrase "since his transfer" points to a past event whose effect is still relevant now.
For such a time marker, the main clause should be in the present perfect tense: "has not visited."
The subject "my brother" is singular, so the auxiliary "has" is correct, not "have."
Option A (
had not been visiting) is past perfect continuous, which needs a past reference point.
Option B (
did not visit) is simple past and does not fit with "since."
Option D (
had not visited) is past perfect, also used only for an action completed before another past action.
Therefore, the correct choice is option C.
Answer:C. has not visited