火场有主要有哪些危害因素？
参考答案：
（1）缺氧：火场上，由于可燃物消耗掉了氧气，使氧含量下降。当氧气在空气中的含量下降到15%时，人体的肌肉协调受影响；下降至14%—10%，判断力会明显减退；下降到10%—6%时，呼吸及心脏同时衰竭，数分钟内可死亡。
（2）高温：只要吸入的气体温度超过70摄氏度，就会使气管、支气管内黏膜充血起水泡，组织坏死，引起肺水肿而窒息死亡。
（3）烟尘：火场上的热烟尘被吸入呼吸系统后，能堵塞、刺激内黏膜，有些甚至能威胁生命
（4）毒气：火灾现场对绝大多数受灾者来说，首先遇到的敌人是烟雾和毒气，而不是高温和熊熊烈火。
根据短文内容,从下框的A-F 选项中选出能概括每一段主题的最佳选项.选项有一项为多余项。
methods and non-standardized curricula (课程), no two courses are the same. Undergraduate courses are considerable different from graduate courses. The classroom atmosphere in expensive, private universities may differ from that in community colleges, which are free and open to everyone.
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.
merely for students to pass exams.) The ideal student is considered to be one who is motivated to learn for the sake of learning, not the one interested only in getting high grades.
Plagiarizing (抄袭) in written work, presenting other's ideas as original, and turning in homework completed by someone else are all prohibited (禁止).
Relationships between students in the classroom can be cooperative or competitive. International |