问题 单项选择题

实验中常用枸橼酸钠抗凝血,其机制是

A.抑制凝血酶的活性

B.加强抗凝血酶Ⅲ的作用

C.防止血小板激活

D.整合血浆中的Ca2+

答案

参考答案:D

解析:
血液凝固的多个环节中都需要 Ca2+的参加,故通常用枸橼酸钠、草酸铵和草酸钾作为体外抗凝剂,它们可与Ca2+结合而除去血浆中的Ca2+,从而起抗凝作用。由于少量枸橼酸钠进入血液循环不致产生毒性,因此常用它作抗凝剂来处理输血用的血液。维生素K拮抗剂,如华法林可以抑制FⅡ、FⅦ、FⅨ、FⅩ等维生素K依赖性凝血因子的合成,在体内具有抗凝作用。肝素在体内、体外均能立即发挥抗凝作用,已广泛应用于临床防治血栓形成。

阅读理解

One morning, Wu Li discovered that her classroom had changed. She found that the desks were no longer in rows(排), but pushed together to make eight bigger desks. She was too excited about it for the first two days and she couldn’t listen to the teachers carefully. But soon she and her classmates got used to this new classroom arrangement (安排). “Now our class is quieter,” said Wu. “What’s more, we can come up with our own ideas and learn more through discussion. It’s a better way to study.”

Li Yu liked it, too. He said, “Group members first discuss, and then show ourselves in front of the whole class. It makes us believe in ourselves.” It was part of a reform (改革) at Li’s school—Baita Secondary School. The school made this reform because they wanted to provide students with easier ways to study and more chances to discuss. “Our school hopes it can improve students’ abilities (能力) to study by themselves and work in groups,” said Zhang Yong, the principal of the school.

However, the reform has demanded (要求) more from teachers. Now they have only about 15 minutes to give the lesson which should be taught in 45 minutes before. It is difficult to teach in such a short time. The teachers have to find better ways to teach more effectively.

“The reform demands more, but I’m sure it is helpful,” added Mr Zhang.

小题1:After the new classroom arrangement it was easier for Wu Li and her classmates to ______ in class.

A.discuss with each other

B.sit in the classroom

C.push desks together

D.teach a lesson小题2:The school made the reform to provide students with _______ to study.

A.noisier classes

B.easier ways

C.more seats

D.fewer chances小题3:The Chinese meaning of the word “effectively” in this passage is _________.

A.简单地

B.明确地

C.有效地

D.认真地小题4:The teachers __________ after the reform.

A.have to find better ways to teach

B.find it easier to teach

C.spend 45 minutes explaining to the students

D.are happy to explain for only 15 minutes小题5:The best title of this passage may be “________”.

A.Students’ Friendship

B.Teachers’ Hope

C.Discussion in Class

D.New Look in Class

单项选择题