如图所示，金属平板P的中垂线上放置正点电荷Q，比较金属平板上a、b、c三点场强方

新设备启动前必须具备（）条件。

A.设备验收工作已结束，生产准备工作已就绪

B.所需资料已齐全，并以书面形式提供有关单位

C.与调度部门已签订并网调度协议

D.调度通信、自动化设备准备就绪，计量点明确，计量系统准备就绪

退休前加入他国国籍同时丧失中国国籍的被保险人，应如何处理其养老保险关系？

绝缘手套、绝缘鞋、绝缘靴分别用于哪些场合？

Largely for "spiritual reasons", Nancy Manos started home-schooling her children five years ago and has studiously avoided public schools ever since. Yet last week, she was enthusiastically enrolling her 8-year-old daughter, Olivia, in sign language and modern dance classes at Eagleridge Enrichment—a program run by the Mesa, Ariz. , public schools and taught by district teachers. Manos still wants to handle the basics, but likes that Eagleridge offers the extras, "things I couldn’t teach. " One doubt, though, lingers in her mind. why would the public school system want to offer home-school families anything

A big part of the answer is economics. The number of home-schooled kids nationwide has risen to as many as 1.9 million from an estimated 345,000 in 1994, and school districts that get state and local dollars per child are beginning to suffer. In Maricopa County, which includes Mesa, the number of home-schooled kids has more than doubled during that period to 7,526, at about $ 4,500 a child, that’s nearly $ 34 million a year in lost revenue.

Not everyone’s happy with these innovations. Some states have taken the opposite tack. Like about half the states, West Virginia refuses to allow home-schooled kids to play public-school sports. And in Arizona, some complain that their tax dollars are being used to create programs for families who, essentially, eschew participation in public life. "That makes my teeth grit," says Daphne Atkeson, whose 10-year-old son attends public school in Paradise Valley. Even some committed home-schoolers question the new programs, given their central irony., they turn home-schoolers into public-school students, says Bob Parsons, president of the Alaska Private and Home Educators Association. "We’ve lost about one third of our members to those programs. They’re so enticing. "

Mesa started Eagleridge four years ago, when it saw how much money it was losing from home schoolers—and how unprepared some students were when they re-entered the schools. Since it began, the program’s enrollment has nearly doubled to 397, and last year the district moved Eagleridge to a strip mall (between a pizza joint and a laser-tag arcade). Parents typically drop off their kids once a week; because most of the children qualify as quarter-time students, the district collects $ 911 per child. "It’s like getting a taste of what real school is like," says 10-year-old Chad Lucas, who’s learning computer animation and creative writing.

Other school districts are also experimenting with novel ways to court home schoolers. The town of Galena, Alaska, (pop. 600) has just 178 students. But in 1997, its school administrators figured they could reach beyond their borders. Under the program, the district gives home-schooling families free computers and Internet service for correspondence classes. In return, the district gets $ 3,100 per student enrolled in the program—$ 9.6 million a year, which it has used partly for a new vocational school. Such alternatives just might appeal to other districts. Ernest Felty, head of Hardin County schools in southern Illinois, has 10 home-schooled pupils. That may not sound like much— except that he has a staff of 68, and at $ 4,500 a child, "that’s probably a teacher’s salary," Fehy says. With the right robotics or art class, though, he could take the home out of home schooling.

In the opening paragraph, the author introduces his topic by（）

A. posing a contrast

B. justifying an assumption

C. explaining a phenomenon

D.making a comparison

下列关于不同耐火等级民用建筑防火分区的最大允许建筑面积说法正确的是（）。

A.一级、二级耐火等级的高层民用建筑防火分区的最大允许建筑面积为1500m²

B.一级、二级耐火等级的单、多层民用建筑防火分区的最大允许建筑面积为3000m²

C.一级耐火等级的地下或半地下建筑（室）防火分区的最大允许建筑面积为400m²

D.三级耐火等级的单层、多层民用建筑防火分区的最大允许建筑面积为1200m²

E.四级耐火等级的单层、多层民用建筑防火分区的最大允许建筑面积为600m²