Option B

Check with the other answers. It doesn't go with it. But check option B -

I have been working ever since I passed out of college.

The correct preposition to fill in the blank is "since".
Explanation:
Here's a detailed explanation of why "since" is the correct preposition in this sentence:
1. The sentence talks about a period of time that started in the past and is still ongoing.
2. The word "ever" indicates that the action of working has been continuous.
3. The phrase "I passed out of college" indicates a specific point in time when the action started.
4. When we want to express the starting point of an action that continues until the present moment, we use the preposition "since".
Therefore, the correct preposition to use in the sentence is "since".
Let's see the options given and eliminate the ones that are not correct:
A: "after" - This preposition implies that the action of working started only after the person passed out of college. It does not indicate a continuous action from that point onwards, so it is not the correct choice.
B: "since" - This is the correct preposition to use. It indicates that the action of working started at the point of passing out of college and has continued until now.
C: "before" - This preposition suggests that the action of working happened before the person passed out of college, which contradicts the context of the sentence. It is not the correct choice.
D: "until" - This preposition implies that the action of working will continue until the person passes out of college. It does not convey the meaning of a continuous action from the point of passing out of college until the present moment. Therefore, it is not the correct choice.
In conclusion, the correct preposition to fill in the blank is "since" (option B).