六级冲刺练习：阅读（105）

　　Some institutions of higher learning offer only the four-year college program. A university offers graduate or post-college programs, as well. Graduate degrees in fields such as English literature, chemistry, and history are granted by graduate schools of arts and sciences. These schools may offer one- or two-year programs leading to a masters degree , and programs lasting three years or more that lead to the degree of doctor of Philosophy . A candidate for a Ph. D. must meet certain course requirements in his field, pass written and oral examinations, and present a written thesis based on original research. Some universities offer postdoctoral programs that extend study and research beyond the Ph. D.

　　Many universities also have what are called professional schools for study in such fields as law, medicine, engineering, architecture, social work, business, library science, and education. Professional schools differ widely in their requirements for admission and the lengths of their programs. Medical students, for example, must complete at least three years of premedical studies at an undergraduate school before they can enter the three- or four-year program at a medical school. Engineering and architecture students, on the other hand, can enter a four- or five-year professional school immediately upon completion of secondary school.

　　The various disciplines, or fields of study, are organized by department. These departments are staffed by faculty members ranging from full professors to

　　instructors. A full professor has tenure, which is permanent appointment with guaranteed employment at the institution until his retirement. Ranking below the full professors are the associate professors, who may or may not have tenure, depending on the policy of the particular college or university. Next are the assistant professors, who do not have tenure. At the bottom of this academic ladder are the instructors. They are usually young teachers who have just received their doctorates or will receive them shortly. Sometimes graduate students are employed as part-time teaching assistants while they are completing their graduate work.

　　Today almost 5 million men and more than 3 million women attend more than 2500 colleges and universities. Approximately 85 percent of these schools are coeducational, which means that both men and women are enrolled in the same institutions. Colleges range in size from a few hundred students to many thousands. Several universities have more than 20, 000 undergraduate and graduate students on one campus. A number of large state institutions maintain branches on several different campuses throughout the state. Classes vary from seminars, or small discussion groups, of fewer than twenty to large lecture courses for hundreds of students.