导轨面在垂直方向弯曲和水平方向扭曲，用光学平直仪都能测量。

For a 400-year-old art form, opera had a bad fame: overweight actresses singing the words which were hard to understand in one of those romance languages you were supposed to learn in high school. And with tickets costing as much as $145 a performance, opera goers also had a certain appearance in people's mind: rich, well-dressed and old.

But now opera companies around the country are loosening their ties and kicking off their shoes in an attempt to keep opera alive and take it to a younger and not so wealthy audience.

Opera producers have found that to attract this crowd, they need to make the opera closer to common people. Because young people don't or won't come to the opera, companies are bringing the opera to them, giving performances in such unusual places as parks, libraries and public schools.

The Houston Grand Opera's choice is the public library, where it performs “mobile operas” shortened versions(剧本) of child-friendly operas. This summer's production is Hansel ＆ Gretel. By performing smaller versions of large productions, producers are able to make people interested while keeping costs at a reasonable level. The San Francisco Opera, which will be celebrating its 75th anniversary this year, is staging Cinderella free of charge, keeping costs down by employing students from its Young Artists' Training Program.

小题1: Which is the main idea of this passage？

A． Opera is famous for its long history.

B． Opera is only performed for rich people.

C． Opera companies are trying to keep opera alive.

D． Young people are not interested in opera.小题2:The underlined phrase in the second paragraph means ______.

A． breaking up the old rules

B． changing the dresses

C． making the audience at ease

D．advertising themselves小题3:Opera companies prefer to perform short versions because ______ .

A． they can be performed in public libraries

B． short versions are easy to perform

C． it is hard to find long versions

D． they can make more people come to opera小题4:The San Francisco Opera employs students in order to ______.

A． celebrate its 75th anniversary

B． reduce the cost

C． attract young people

D． make Cinderella popular

新鲜冰冻血浆保存1年后，Ⅷ因子下降多少（）。

A.95%

B.85%

C.75%

D.65%

E.55%

预约定价协议

验槽的方法有（）

A.表面验槽法

B.钎探检查验槽法

C.洛阳铲探验槽法

D.开挖验槽法

E.锤击验槽法

政协有哪些特点和优势？