小静想：白球碰撞后立即静止，被撞的球是以白球撞前相同大小速度运动出去的吗？

通过了解和初步实验，小静发现只有当体积和质量均相同的两球，而且球心在同一直线上相碰时，才可能出现上述现象。为进一步探究，她设计了下述实验方案：

将一个两端翘起、中间水平的轨道固定在水平桌面上，取两个相同的台球A、B，将B球静置于轨道的水平部分，A球置于轨道左端斜面上某处，测出该点到水平桌面的高度h₁，如图乙所示，释放A球，撞击后，A球静止，B球向前运动并冲上轨道右端斜面能到达的最高点，测出该点的高度h₂。通过比较h₂与h₁的大小关系即可作出判断．请你作答以下问题：

    Vandna loved sports and did well in her lessons at her high school in California. When a headache disturbed the 15-year-old girl's walk to class, she 1 it.

    “It was 2.” she thought, “Just a headache—harmless”

But when walking to her next class, she was 3 and collapsed to the floor. 4 she could hear other talking, she couldn't speak. She was 5 to the hospital in an ambulance. Tests indicated Vandna had a stroke affecting the right side of her brain, thus affecting the 6 side of her body.

    What was worse, the stroke caused her brain to began to swell, and she needed operation to 7 the pressure the swelling was putting 8 her brain. The doctors 9part of her skull（头骨）to make room for the swelling. 10 the swelling went down（消退）, her skull was placed back again.

    While the doctors predicted that she would never live a normal life, Vandna 11 improved. She was in a rehab center（康复中心）for about 3 months and began to realize how 12 her daily life might be. She had to wear a brace（支架）on her left leg to support her 13. Her left arm 14 lightly, and she often became tired. Though 15 on a campus wasn't easy, she finished high school and 16 a degree in speech therapy at University of Redlands.

    After the stroke, Vandna became 17 with the American Heart Association. She shared her 18 at public events and urged others to stay 19. She said if you 20 a tough time, remember tough times don't last, but tough people do.

设a＝$\sqrt{7}$−1，则代数式a²+2a-12的值为（　　)

著名的佛教建筑﹣﹣吴哥窟位于（　　）

下列做法中，未注意食品安全的是（　　）