如图，△ABC中，D为BC上一点，△ABD的周长为12cm，DE是线段AC的垂直平分线，AE＝5cm，则△ABC的周长是（　　　）

有一个高大的五棱柱形建筑物，人站在地面上，不可能同时看到的是（　　）

在空间中，“经过点P（x₀，y₀，z₀），法向量为$\overrightarrow{e}$=(A,B,C)的平面的方程（即平面上任意一点的坐标（x，y，z）满足的关系）是：A（x﹣x₀）+B（y﹣y₀）+C（z﹣z₀）=0”．如果给出平面α的方程是x﹣y+z=1，平面β的方程是$\frac{x}{6}-\frac{y}{3}-\frac{z}{6}=1$，则由这两平面所成的二面角的正弦值是（　　）

Complete the sentences with the given words in their proper forms (用括号中所给单词的适当形式完成下列句子。每空格限填一词)
Climb up to the ____ floor, and you can enjoy a better view. (eleven)
____ , Grace made up her mind to live abroad with her daughter. (final)
It is a very ____ book for language learners to improve writing skills. (use)
Don't worry about your son. He is old enough to be independent and live by ____ . (he)
The movie KungFu Panda II is sure to ____ a large number of teenagers. (attractive)
If you don't go on a diet, it is ____  for you to lose weight. (possible)
The local people had to move away because of the serious ____. (pollute)
The great ____  gave his first show in Shanghai and the tickets sold out in minutes. (art)