某大型综合利用水利水电枢纽工程位于峡谷地区，基岩完整、坚硬、岸坡陡峻，该工程泄流的消能方式宜采用______。
A．底流消能
B．挑流消能
C．面流消能
D．消力戽消能
参考答案：B
解析： (1)挑流消能适用于坚硬岩基上的高、中坝。(2)底流消能是利用水跃消能，多用于低水头、大流量、地质条件较差的泄水建筑物。(3)面流消能适用于中、低水头工程尾水较深，流量变化范围小，水位变幅较小，或有排冰、漂木要求的情况。一般不需要作护坦。(4)消力戽消能是利用泄水建筑物的出流部分造成具有一定反弧半径和较大挑角所形成的戽斗，在下游尾水淹没挑坎的条件下，形不成自由水舌，高速水流在戽斗内产生激烈的表面旋滚，后经鼻坎将高速的主流挑至水面。并通过戽后的涌浪及底部旋滚而获得较大的消能效果。适用于尾水较深，流量变化范围较小，水位变幅较小，或有排冰、漂木要求的情况。一般不需要作护坦。
| At the beginning of the twentieth century, North American society held, as an ideal, the Nuclear Family. This presumably perfect residential, social, and economic unit consisted of an adult male, an adult female and their minor children. This structure was thought to be stable and long lasting. However, a few decades later, the structure of that ideal family was being altered radically even while it was being touted as the structure to be aimed for. Popular magazines bemoaned the loss of the Nuclear Family and its replacement with inferior forms. There are a number of factors that are acting in concert to apply pressure on the Nuclear Family and generate a variety of new structures. Some of these are: The definition of marriage has changed somewhat in that few people now consider it to last "until death do us part." The concept of monogamy (the marriage of one man and one woman) has been modified to a form now referred to as serial monogamy (the marriage of one man and one woman at a time). This reflects the increasing equality of women and men in terms of economic advantage and the recognition that many women no longer depend on men for their survival. Women are acquiring independence and have become empowered to make their own choices. With this independence, the need to form a relationship with a man becomes less important. This change embodies the concept that the marriage is temporary and can be terminated by either partner at any time. Associated with this, of course, is the relaxation of the divorce laws and the significant reduction of the shame that had one time been attached to divorce. The economy of North America has resulted in a two-tier system of a few rich who control most of the resources and a large portion of the population who control almost none of the resources. Because of this, many couples are forced to have both partners with full-time jobs outside the home. There are unintended byproducts of the need for a double income. The most important of these is the replacement of a mother-oriented socialization of children to a "stranger-oriented" socialization system reflected in the growth of the childcare industry. Also, either partner is financially able to end the marriage without significant hardship. The combination of these changes will in the coming decades have a profound effect on the structure of the family of North America. As a result, the family will be a fluid, constantly changing structure with variable household arrangements as the norm. |
What has changed the Nuclear Family in North America
A．People have changed their ideas about marriage.
B．Women become more independent.
C．The economy is changing.
D．All of the above factors are acting together.