Explanation:
When answering this question, it is important to understand the meaning and usage of the words given as options. Let's break down each option:
Option A: "after"This word indicates that the person started working after they passed out of college. However, the original sentence does not convey this meaning, as it says "ever since" instead of "ever after". Therefore, option A is not the correct answer.
Option B: "since"This word is used to show that the person started working at the same time they passed out of college, and they have been working continuously since then. This fits perfectly with the original sentence, making option B the correct answer.
Option C: "before"This word indicates that the person started working before they passed out of college. However, the original sentence does not convey this meaning, as it says "ever since" instead of "ever before". Therefore, option C is not the correct answer.
Option D: "until"This word indicates that the person stopped working when they passed out of college. However, the original sentence does not convey this meaning, as it says "ever since" instead of "ever until". Therefore, option D is not the correct answer.
In conclusion, the correct answer is option B: "since". This word accurately reflects the meaning of the original sentence, indicating that the person has been working continuously since they passed out of college.