Read the following passage and mark the letter A,B,C or D on your answer sheet to indicate the correct answer to  each of the questions from 35 to 44

Course numbers are an indication of which courses are to various categories of students at the University. Undergraduate courses with the numbers 100 or 200 are generally courses with the numbers 300 or 400 often have prerequisites and are often to juniors and seniors only. Courses with the numbers 800 or above are open only to graduate students. Certain graduate courses, generally those devoted to introductory material, are numbered 400 for undergraduate students who qualify to take them and 600 for graduate students. Courses designed for students seeking a professional degree carry a 500 number for undergraduate students and a 700 number for graduate students. Courses numbered 99 or below are special interest courses that do not carry academic credit. If students elect to take a special interest course, it will not count toward the number of hours needed to complete graduation requirements.

Full-time undergraduate student is expected to take courses that total twelve to eighteen credit hours. A full-time graduate student is expected to take courses that total ten to sixteen credit hours. Student holding assistantships are expected to enroll for proportionately fewer hours. A part-time graduate may register for minimum of three credit hours. An overload, that is, more than the maximum number of hours, may be taken with the approval of an academic advisor. To register for an overload, students must submit the appropriate approval form when registering. Overloads above 24 hours will not be approved under any circumstances.(Source: Practice Exercises for the TOEFL iBT, by Pamela J. Sharpe, Ph.D)

The word "categories" in paragraph 1 is closest in meaning to______.