降低稀镁含硝主要操作措施是（）和保证浓镁浓度。A.保持硝镁加热器一定温度 B.及时调

动物通过呼吸作用将体内的一部分有机物分解成无机物，这体现了动物在自然界中的哪项作用（　　）

A．维持生态平衡

B．促进生态系统中的物质循环

C．帮助植物传粉

D．帮助植物传播种子

B

For a 400-year-old art form, operas had a bad fame: overweight actresses singing the words which are 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 have 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 bring the opera to the audience. It needs to keep it alive, the young and not-so-rich.

Opera producers have found that to attract this crowd, they need to make the opera closer to common people. That means no formal suits, old-styled theatre or band-breaking ticket prices. And 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.   

45．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．Young people are not interested in opera.                              

D．Opera companies are trying to keep opera alive.

46．The underlined phrase “loosening their ties and kicking off their shoes” (paragraph 2) means ______.

A．breaking up the old rules                      B．changing the formal suits

C．making the audience at ease                  D．advertising themselves

47．The San Francisco Opera Company employs student actors in order to ______.

A．celebrate its 75th anniversary                B．reduce the cost

C．attract young people                             D．make Cinderella popular

48．From the passage we can infer that ______.

A．the tickets for operas are very expensive                               

B．operas are performed in a difficult language

C．operas are not so popular an art form today                           

D．students enjoy performing operas very much

诊断急性肾小球肾炎最有意义的临床表现为（）。

A.水肿

B.高血压

C.蛋白尿

D.血尿

E.低比重尿

炉中钎焊时，在停炉后应打开炉门或放散管，排除炉内残存的可控气氛，或用（）吹扫。

A.活性气体

B.惰性气体

C.氧气

补气药的性味以甘温或甘平为主，其中兼能燥湿者，还可有（）味。补阴药的性味以（）为主，大多有一定滋腻性。