I don't know how to answer part a

Question 3 Candy is a Year 4 full-time undergraduate student majoring in marketing at a private university in Hong Kong and she is going to be graduated after the summer break. She has collected some data from the Student Careers and Affairs Office (SCAO) related to her job planning. According to the graduate employment surveys conducted for the last two years by the private university, the average salary earned by the graduates of her programme is constant at around $14,000. Actually, Candy is quite disappointed. In view of this, Candy is considering to participate in an one-year internship program launched by the SCAO after her graduation. In other words, she would enter the job market "formally" one year later if she joins the internship program. Finally, with the help of the SCAO, she could get an internship offer from a famous marketing company in Hong Kong. The monthly salary provided by the company is $12,000 while a good reference letter would be prepared for the interns completing the internship satisfactorily. With this good reference letter and sound working experience gained, Candy hopes she could be more competitive in the job market with the profile of internship. Candy now is considering whether to accept the internship offer of the marketing company. (a) Define opportunity cost. What is the opportunity cost for Candy to accept the internship offer of the marketing company? Explain