Explanation
The correct option to complete the sentence is:
B) since
Explanation: The correct sentence would be "I have not seen him since last Wednesday." The word "since" is used to indicate a point in time in the past from which the action (not seeing him) continues up to the present. It implies that the speaker has not encountered or had any visual contact with the person since the mentioned Wednesday. Option A) for (used to indicate a duration of time) and Option D) from (used to indicate the starting point of an action) do not convey the same meaning as "since" in this context. Option C) about does not fit the sentence grammatically or contextually.
