据科学家预测，月球的土壤中吸附着数百万吨的
He，每百吨He核聚变所释放出的能量相当于目前人类一年消耗的能量。在地球上，氦元素主要以
He的形式存在。下列说法正确的是( )。
A．He原子核内含有4个质子
B．He和He互为同位素
C．He原子核内含有3个中子
D．He的最外层电子数为2，所以He具有较强的金属性
答案：B
本题的解题关键在于熟悉原子的表示符号
X，A表示质量数，Z表示质子数，所以可判断A、C错误；又
He的最外层电子数为2，虽然少于8个，但属于稳定结构，因此D选项错误。
| 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. |
Many wives work outside their home because they______.
A．want to be independent
B．don’t want to stay at home
C．don’t have to take care of their children
D．want to make money for their home