The Correct answer is Option 4. Explanation & Key Takeaways: The passage clearly brings out the understanding that brain drain harms developing countries in two major ways. • Statement (a) is correct because the passage explains that developing countries spend huge amounts on educating technicians, scientists, engineers, and doctors at nominal cost, but do not get any return on this investment when they migrate. • Statement (d) is also correct as the passage explicitly states that due to brain drain, the tempo of development of poor countries slackens, creating obstacles to their development. • Statement (b) is incorrect because the passage does not mention population decline as a disadvantage of brain drain. • Statement (c) is also incorrect since the passage does not discuss population-related problems in receiving countries as a disadvantage. Therefore, the correct answer is Option 4: Only a and d.