Student participation(参与) in the classroom is not only accepted but also expected of the student in many courses．Some professors base part of the final grade on the student' s oral participation．Although there are formal lectures during which the student has a passive role (i．e．, listening and taking notes),
many courses are organized around classroom discussions, student questions, and informal lectures．In graduate discussions the professor has a "manager" role and the students make presentations and lead discussions．The students do the actual teaching in these discussions．
A professor' s teaching method is another factor (因素) that determines the degree and type of student participation．Some professors prefer to control discussion while others prefer to guide the class without controlling it．Many professors encourage students to question their ideas．Students who object to the professor' s point of view should be prepared to prove their positions．
In the teaching of science and mathematics, the controlling mode of instruction is generally traditional ,with teachers presenting formal lectures and students taking notes．However, new educational trends have turned up in the humanities and social sciences in the past twenty years．Students in education, society, and history classes, for example, are often required to solve problems in groups, design
projects, make presentations, and examine case studies．Since some college or university courses are"practical" rather than theoretical ,they pay more attention to "doing" for themselves．
The reason why some professors ask students to make presentations and lead discussions is that_______．
推理判断题。最后一段最后一句指出，一些大学的课程是实践课而不是理论课，所以一些教授让学生们在课堂上做陈述和讨论的时候，他们想要去强调“做”。
把10gMgCl2和MgSO4的混合物溶于适量水中，滴加2mol／L的BaCl2溶液至沉淀完全，共消耗BaCl2溶液25mL。求混合物中MgCl2和MgSO4的质量各是多少克
固定在匀强磁场中的正方形导线框abcd，各边长为1．其中ab是一段电阻为R的均匀电阻丝，其余3边均为电阻可忽略的铜线。磁场的磁感应强度为B，方向垂直纸面向里。现有一与ab段的材料、粗细、长度都相同的电阻丝PQ架在导体框上，如图所示。PQ以恒定速度方向如何
一小物块以速度v0=10m／s沿光滑地面滑行，然后沿光滑曲面上升到顶部水平的高台上，并由高台上飞出，如图所示。问当高台的高度h多大时，小物块飞行的水平距离最大这个距离是多少(g=10m／s2)
某晶体盐的水溶液呈浅绿色，在此溶液中通入氯气，溶液变为棕黄色，把所得棕黄色溶液分成两份：一份加入KSCN溶液，溶液变深红色；另一份加入BaCl2溶液，产生不溶于稀HNO3的白色沉淀，则该晶体盐的化学式是_______。
欲除去乙烷中的乙烯，可将混合气体通过盛有_______的洗气瓶；欲除去乙炔中的硫化氢，可将混合气体通过盛有_______的洗气瓶。
浓硝酸常盛装在棕色瓶中，且贮放在冷暗处，原因是_______，
碳酸氢钠溶液和烧碱溶液反应的离子方程式为_______。
常温下，氨水中存在的离子有_______。
在酸或碱存在的条件下，甲酸甲酯跟水发生水解反应的化学方程式为_______。
有下列几种气体：H2、O2、HCl、NO、NH3、CH4，其中通常情况下能用来和水做“喷泉”实验的是_______。
