简述采用滤膜测尘法检测隧道内粉尘浓度的原理与测定过程。

下列对2004年1～12月份主要机械产品产量描述不正确的是（）。

A．2004年1月以来，机械整体仍保持较高的增长速度

B．小型拖拉机产量在2004年全年呈负增长趋势，市场低迷

C．大中型拖拉机市场的火爆，反映出农民收入明显提高，购买力增强

D．2004年饲料加工机械产量呈负增长趋势

引起子痫抽搐的主要病理原因是（）

A.颅内脑组织散在出血点

B.颅内小动脉痉挛，脑水肿

C.血钙低下

D.代谢性酸中毒

E.高血压

预热枪的枪位最低下限位置（）cm。

A.300

B.400

C.450

D.500

More surprising, perhaps, than the current difficulties of traditional marriage is the fact that marriage itself is alive and thriving. As Skolnick notes, Americans are a marrying people: Relative to Europeans, more of us marry and we marry at a younger age. Moreover, aster a decline in the early 1970s, the rate of marriage in the United States is now increasing. Even the divorce rate needs to be taken in this pro-marriage context: some 80 percent of divorced individuals remarry. Thus, marriage remains, by far, the preferred way of life for the vast majority of people in our society.

What has changed more than marriage is the nuclear family. Twenty-five years ago, the typical American family consisted of a husband, a wife, and two or three children. Now, there are many marriages in which couples have decided not to have any children. And there are many marriages where at least some of the children are from the wife’s previous marriage, or the husband’s, or both. Sometimes these children spend all of their time with one parent from the former marriage; sometimes they are shared between the two former spouses.

Thus, one can find the very type of family arrangement. There are marriages without children; marriages with children from only the present marriage; marriages with "full-time" children from the present marriage and "part-time" children from former marriages. There are step-fathers, step-mothers, half-brothers, and half-sisters. It is not all that unusual for a child to have four parents and eight grandparents! These are enormous changes from the traditional nuclear family. But even so, even in the midst of all this, there remains one constant: Most Americans spend most of their adult lives married.

Even though great changes have taken place in the structure of American families, （）

A. the functions of marriage remain unchanged

B. most Americans prefer a second marriage

C. the vast majority of Americans still have faith in marriage

D. all of the above

导游人员将重病患者送往医院或急救中心，需由患者的______、______或领队陪同前往，若需动手术时，可以请他们签字。