Question 20 is based on the passage you have just heard.

    If you are a graduate student, you may depend on your adviser for many things, including help with improving grades, acquiring financial support, forming an examining committee and getting letters of recommendation. If you‘re a graduate teaching assistant, your adviser also may be your boss. （19）Academic departments vary in their procedures for assigning academic advisers to graduate students. In some departments, either the chairman or the director of graduate studies serves for at least the first semester as a new student adviser. Then students select an adviser  based on shared academic interests. In other departments, a new student is assigned a faculty adviser based on some system of distribution of the department’s advising load. Later, students may have the opportunity of selecting the adviser that they prefer.（20）In any case, new graduate students can learn who their advisers or temporary advisers are by visiting or emailing the departmental office and asking for the information. （21）Graduation requirements specify the number of credits you must earn, the minimum grade point average you must achieve and the distribution of credits you must have from among differing departments or fields of study. In addition, it is necessary to apply for graduation when you are near the time that you will be completing your graduation requirements. Since graduation requirements vary among divisions of the university, you should consult the Bulletin of Information. You should also direct your questions to your departmental office or academic adviser.

20. How can new graduate students learn who their advisers are?

原文中提到研究生新生可以通过直接拜访或邮件方式到系办公室了解自己的导师的相关信息，“by visiting or emailing the departmental office”，对应选项D）By contacting the departmental office，两者属于同义替换， 故正确答案为 D。