[单项选择]二氧化碳气体保护焊时，如果气体保护层被破坏，则易产生（）气孔。
A. 一氧化碳
B. 二氧化碳
C. 氮气
D. 氢气

N-ISDN是在 (33) 基础上建立起来的网络，能够提供的最高速率是 (34) 。网络提供基本接口速率时，传输声音需要使用 (35) ，一路话音占用的数据传输数率是 (36) ，占用户实际可用带宽的比例是 (37) 。

（二）阅读下面的材料，回答第135~138题： 我国国民经济和社会发展第十个五年计划指出，世纪之交，我国胜利实现了现代化建设的第二步战略目标，经济和社会全面发展，人民生活总体上达到了小康水平。从新世纪开始，我国将进入全面建设小康社会，加快推进社会主义现代化的新的发展阶段。……经过二十多年的改革开放和发展，我国社会生产力、综合国力和人民生活水平都上了一个大台阶，市场供求关系、体制环境和对外关系发生了重大变化，为开始实施现代化建设第三步战略部署奠定了良好的基础。

Some recent historians have argued that life in the British colonies in America from approximately 1763 to 1789 was marked by internal conflicts among colonists. Inheritors of some of the viewpoints of early twentieth century Progressive historians such as Beard and Becker, these recent historians have put forward arguments that deserve evaluation. The kind of conflict most emphasized by these historians is class conflict. Yet with the Revolutionary War dominating these years, how does one distinguish class conflict within that larger conflict Certainly not by the side a person supported. Although many of these historians have accepted the earlier assumption that Loyalists represented an upper class, new evidence indicates that Loyalists, like rebels, were drawn from all socioeconomic class. (It is nonetheless probably true that a larger percentage of the well-to do joined the Loyalists than joined the rebels.) Looking at the rebels side, we find little evidence for the contentio
A. These conflicts were instigated by eastern interests against western settlers.
B. These conflicts were the most serious kind of confliet in America.
C. These conflicts eventually led to openly expressed class antagonism.
D. These conflicts contained an element of class hostility.