设B={P, Q}, 则B 上可以定义 (55) 个等价关系。A．2 B．3 C

“古人学问无遗力，少壮工夫老始成。纸上学来终觉浅，绝知此事要躬行。”这是我国诗人陆游的诗作。这首诗对我们培养自立能力和自强精神启示是（ 　 ）

A．要认真学习，明白自立自强的道理

B．要认真思考，明白自己的长处和短处　　

C．要学习别人自立自强的经验

D．要多实践、多锻炼，培养自立自强精神

阅读下面一首元曲，回答下题。（12分）

【正宫】塞鸿秋·山行警

张鸣善

东边路西边路南边路，五里铺七里铺十里铺。行一步盼一步懒一步，霎时间天也暮日也暮云也暮。斜阳满地铺，回首生烟雾，兀的不山无数水无数情无数。

1、这首元曲题为“山行警”，联系全曲，是借“山行”警示了人们什么？（4分）

2、“天也暮日也暮云也暮”“斜阳满地铺”，表面上写的是时近傍晚，实际上写的是什么？（4 分）

3、“回首生烟雾，兀的不山无数水无数情无数”，其深层含义是什么？（4分）

等离子弧的温度可达（）。

A、5000-10000摄氏度

B、15000-3000摄氏度

C、30000-35000摄氏度

若橡套电缆的电缆截面为25～35（mm2），在对其进行冷压连接时连接芯线绝缘切割长度为（）。

A、50mm

B、170mm

C、200mm

D、240mm

There has been much speculation about the origin of baseball. In 1907 a special commission decided that the modern game was invented by Abner Doubleday in 1839. One hundred years later the National Baseball Museum was opened to honor Doubleday. Historians, however, disagree about the origin of baseball. Some say that baseball comes from bat-and-ball games of ancient times. It is a matter of record that in the 1700s English boys played a game they called "baseball". Americans have played a kind of baseball since about 1800. At first the American game had different rules and different names in various parts of the country — "town ball", "rounders", or "one old cat". Youngsters today still play some of these simplified forms of the game.Baseball did not receive a standard set of rules until 1845, when Alexander Cartwright organized the Knickerbocker Baseball Club of New York City. The rules Cartwright set up for his nine-player team were widely adopted by other clubs and formed the basis of modern baseball. The game was played on a "diamond" infield with the bases 90 feet apart. The first team to score 21 runs was declared the winner. By 1858 the National Association of Baseball Players was formed with 25 amateur teams. The Cincinnati Red Stockings began to pay players in 1869.

What was the first professional baseball team called

A．New York Knickerbockers.

B．Milwaukee Braves.

C．Cincinnati Red Stockings.

D．Brooklyn Dodgers.