根据下面资料，回答下列各题 On the evening before All Saints Day in 1517, Martin Luther nailed 95 theses to the door of a church in Wittenberg. In those days a thesis was simply a _____36_____ one wanted to argue. Today a doctoral thesis is both an idea and an _____37_____ of a period of original research. Writing one is the aim of the hundreds of thousands of students who _____38_____ on a doctorate of philosophy (PhD) every year. In most countries a PhD is a basic requirement for a career in academia. It is an introduction to the world of independent research-a kind of _____39_____ masterpiece, created by an apprentice in close collaboration with a supervisor. The requirements to complete one vary _____40_____ between countries, universities and even subjects. Some students will first have to spend two years working on a masters degree or diploma. Some will receive a stipend; others will pay their own way. Some PhDs_____41_____ only research, some require classes and examinations and some require the student to teach undergraduates. A thesis can be dozens of pages in mathematics, or many hundreds in history. As a result, newly minted PhDs can be as young as their early 20s or world-weary forty-somethings. One thing many PhD students have in common is _____42_____. Some describe their work as 'slave labour'. Seven-day-weeks, ten-hour days, low pay and uncertain prospects are widespread. Whining PhD students are nothing new, but there seem to be _____43_____ problems with the system that produces research doctorates (the practical 'professional doctorates' in fields such as law, business and medicine have a more obvious value), There is an oversupply of PhDs. Although a doctorate is designed as training for a job in academia, the number of PhD positions is unrelated to the number of job openings. Meanwhile, business leaders _____44_____ about shortages of high-level skills, suggesting PhDs are not teaching the right things. The fiercest critics _____45_____ research doctorates to Ponzi or pyramid schemes.