草原生态系统中，营养元素分级的依据是什么？

阅读短文，选择正确答案。

    If there is time for questions or discussion at the end of a class, take the chance to ask for further explanation

of anything that was not immediately clear. You are unlikely to be the only one who does not understand. So

our questions will help others and will encourage them to ask questions, and you should learn from all the

teacher's replies.

    Questions not only help students to learn but also show interest in the subject, and this makes the teacher's

work more useful. Besides, questions should help the teacher first to recognize things that students find difficult

and then to give better lessons. More questions will come to mind during your further studies. Try to find the

answers before the next class. This will help you to learn.

1. The writer of this passage advises us _____. [ ]

A. to ask for further explanation of everything we learn

B. to ask questions at the end of a class

C. to help others by asking the teacher questions

D. to encourage the teacher to give better lessons

2. According to the passage, you ask questions in order to ____. [ ]

A. make your teacher recognize you

B. encourage your school friends to learn better

C. make yourself and your classmates learn better

D. satisfy your teacher

3. According to the passage, questions are helpful _____. [ ]

A. either to the slow students or to the bright students

B. to both the teachers and the students

C. neither to the teachers nor to the students

D. especially to some teachers

高血钾可导致酸中毒的原因可能是（）

A.K⁺促进葡萄糖酵解成乳酸

B.肾小管细胞H⁺与Na⁺的交换增加，导致血浆[H⁺]减少

C.K⁺抑制肾的糖异生，间接减少铵盐生成

D.血浆K⁺与细胞内H⁺交换，使血浆[H⁺]升高

E.K⁺促进脂肪动员，生成酮体

承包人运至施工现场的施工机具是承包人的财产，他有权使用到本合同之外的其他项目施工中去。

医疗机构审核和调配处方的药剂人员必须是（）

A．执业药师或者其他依法经资格认定的药学技术人员

B．从业药师或者其他依法经资格认定的药学技术人员

C．主任药师或者其他依法经资格认定的药学技术人员

D．主管药师或者其他依法经资格认定的药学技术人员

E．依法经资格认定的药学技术人员

视路包括下述组织，除了：（）

A.视网膜

B.视神经

C.视交叉、视束

D.外侧膝状体、视放射

E.视中枢