如果横轴表示商品Y的消费量，纵轴表示X的消费量，预算约束线围绕与横轴的交点旋转，说明

在括号里填上恰当的词语。

一（　　）骆驼　　一（　　）显微镜

在初步设计阶段编制工程概算所采用的一种定额，是以整个建筑物或构筑物为对象，以“m²”、“m³”或“座”等为计量单位规定人工、材料、机械台班耗用量的数量标准是( )。

A．施工定额
B．预算定额
C．概算指标
D．概算定额

More than 6000 children were expelled(开除) from US schools last year for bringing guns and bombs to school, the US Department of Education said on May 8.

The department gave a report on the expulsions as saying handguns accounted for 58 percent of the 6093 expulsions in 1996—1997, against 7 percent for rifles(步枪) or shotguns and 35 percent for other types of firearms.

"The report is a clear sign that our nation’s public schools are cracking down(严惩)on students who bring guns to school", Education Secretary Richard Riey said in a statement, "We need to be tough-minded(坚强的) about keeping guns out of our schools and do everything to keep our children safe. "

In March 1997, an 11-year-old boy and a 13-year-old using handguns and rifles shot dead four children and a teacher at a school in Jonesboro, Arkansas. In October, two were killed and seven wounded in a shooting at a Mississippian school. Two months later, a 14-year-old boy killed three high school students and wounded five in Daducab, Kentucky.

"Most of the expulsions(开除), 56 percent, were from high schools, which have students from about age 13, 34 percent were from junior high schools and 9 percent were from elementary schools. " The report said.

The main idea of Paragraph Four shows us（）.

A．some examples of shootings in US schools

B．the Americans’ feeling

C．some famous schools

D．that some teachers were killed by students

光在某种玻璃中的速度是×10⁸ m/s，若使光由空气射入这种玻璃，且使折射光线与反射光线垂直，则入射角应是（   ）

A．30°

B．60°

C．45°

D．90°

结构型传感器是依靠（）的变化实现信号变换的。