Final answer:
The subject of this question is Social Studies. The correct answer is option A) 480,000 immigrants, with a significant number employed as engineers and nurses.
Step-by-step explanation:
The subject of this question is Social Studies. The question is asking about the characteristics of immigrants living in a certain country in 1999, specifically regarding their professional occupations.
The information provided states that a significant number of the 480,000 immigrants were employed as engineers and nurses, while very few were librarians. Therefore, the correct answer is option A) 480,000 immigrants, with a significant number employed as engineers and nurses.