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一定时期内流通过程中所需要的货币量是：
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College professors are often believed to lead easy lives of quiet thinking while teaching one or two classes every week. But college professors do much more than go to class. The 1._____ professor spends between six and fifteen hours in the classroom 2_____. And that same college professor works from sixty to eighty hours a week.Because they must remain 3_____ in their fields, professors spend part of that time reading, reading, reading. That leads to 4_____ hours during which they revise and 5_____ their class lecture notes. It takes far longer to prepare notes than to deliver them in class. Professors may spend time 6_____ experiments, working on college projects, or 7_____ students. They may be writing books, articles, or papers for delivery at 8_____.When not in the classroom or in the office, professors are still working, behind closed doors in committee 9_____ or at home grading papers and preparing for tomorrow’s classes. To accept this sort of schedule willingly, they must feel strongly about the 10_____ of the college experience.[音频]
1．机体的特异性体液免疫应答主要由____介导。体液免疫应答的第一步是______对抗原的特异性识别及两者的结合。2．B细胞作为抗原呈递细胞，其表面主要的协同刺激分子是______；作为免疫效应细胞，其表面主要的协同刺激分子是______。3．B细胞识别的抗原主要是_______还有____ 。4．在TD抗原诱导的初次应答中，血清抗体持续时间相对______，抗体类型主要为_____；而二次应答中，_____ 类抗体含量较初次应答时显著增高。
男性尿道可分为、、三部，临床上将称为前尿道。
关于生物法除氮过程，以下说法正确的是（）
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