用四舍五入法对数5664935取近似值，保留三个有效数字，结果是______．

采用各种措施来防止各种错畸形的发生为（）

A.预防性矫治

B.阻断性矫治

C.功能性矫治器

D.个别正常

E.暂时性错

小明在厨房发现一种白色固体，他认为“可能是食盐”，小华说“可以尝一尝”．对“可能是食盐”是科学探究过程中的（　　）

A．问题

B．假设

C．实验

D．结论

关于老年性二尖瓣钙化，以下何项不正确()

A．本病可引起二尖瓣狭窄和(或)关闭不全

B．随年龄增长其发病率增高

C．可引起心脏传导阻滞型心律失常

D．本病亦可见于青年人

E．男性发病明显多于女性

你打算让外国朋友了解新落成的国家大剧院的情况，准备在互联网上制作一个介绍中国国家大剧院的网页。请根据下例提示，为网页写一篇短文。词数不少于70.

Where is the National Grand Theatre located?

(the heart of Beijing, west of Tian’anmen Square)

When did the construction begin and when was it completed?

( in December 2001, in September 2007)

What is the area that it covers?

( 35,5000 square meters)

What does it look like surrounded by an artificial lake? (a big egg)

What kind of halls are there inside the theatre? How many seats are there in each hall?

( an opera hall, paint it mainly gold, 2398 seats; and a music hall, paint it white, 2019 seats)

What are your opinions or feelings about the National Grand Theatre?

压力机的主要技术参数有哪些？