压与频率都增加5℅时，穿过铁芯线圈的主磁通（）。A.增加 B.减少 C.基本不变
题型：单项选择题
问题：
压与频率都增加5℅时，穿过铁芯线圈的主磁通（）。
A.增加
B.减少
C.基本不变
题型：单项选择题
任务型读写。
阅读下面短文，并根据所读内容在文章后表格中的空格内填入一个恰当的单词。
The population of the United States is growing older and will continue to do so. According to a report,
39 million Americans will be 65 or older by the year 2010, 51 million by 2020,and 65 million by 2030.
The "graying" of the United States is mainly due to the fact that people in the U.S. are living longer. As
a matter of fact, the number of U.S citizens 85 years old and older is growing six times as fast as the rest
of the population. It is also largely due to the old- growing of the "baby boomers", the generation born after
World War Ⅱ. In 1957,over 4.3 million babies were born. More than 75 million Americans were born between
1946 and 1964,the largest generation in U.S. history. In less than twenty years, millions of them will become
elderly people.
The "graying" of the U. S. will greatly affect the nation's family and workforce. One likely development
will be a gradual change in the family unit; it will move away from the nuclear family and towards a
multigenerational family. The other likely development will be a change in the proportion (比例) of the nation's
workforce. In 1989 there were 3.5 workers for every person 65 or older; by the year 2030, there will only be
2 workers for every person 65 and older.
Title: 1 . U.S.
