发行企业并未将剩余收益分配给股东，而是用于追加投资扩大再生产，在这种假设下，普通股股

下列哪项不是蝗虫的特点（　　）

A．身体由体节构成

B．体表有外骨骼

C．用鳃呼吸

D．足和触角分节

在一次测定引力常量的实验中，已知一个质量为0.8kg的球，以1.3×10^-10N的力吸引另一个质量为4.0×10^-3kg的球，这两个球相距0.04m，求引力常量G。地球表面的重力加速度为9.8m／s²，地球的半径为6400km，求地球的质量。

Surfing—the art of riding a wave on a pointed board—is the wildest, fastest natural water sport known to man. In recent years, it has developed into a major sport around the world, from Australia to South Africa. Australians brave(挑战) men—eating sharks to ride the green waves Down Under, Hawaiian experts risk(冒…之险) their lives on huge, thirty foot swells(浪涛) against the wind of Oahu; Californians of all ages go out the year-round. In the winter, surf-riders put on life-suits to ride grave waves so cold that their flesh turns blue.

Surfing is no sport for weak persons. Swimming a quarter of a mile or more, and pushing a surfboard out to where the swells are just right for riding, can be real work. Then, at exactly the right moment, you climb up the wave and go fast across the face of a powerful swell with the white water jumping at your feet. The huge wave bites at your shoulder, threatening(威胁) at any moment to smash your flat. In the next several seconds, a cool head and lightning—quick action back to the pressure of the attacking wave will bring your board under control for that great ride down the back of the great, green mountain of water. Once on the beach, you know why surfing is growing in popularity as an international sport, and you’re glad to be a member of this new water world.

小题1:The first paragraph mainly tells us ______.

A．people around the world go surfing all the year round

B．the definition(定义) of the sport

C．how to surf in the sea

D．where to surf around the world小题2:The author believes that surfing _______.

A．is not an easy sport

B．can be done by anyone

C．should be done by everyone

D．does not require courage小题3:In order to experience what real surfing is, _______.

A．you must first swim a quarter of a mile to warm your body

B．you will first ride on a board to reach the swells

C．you must first put on your life-suits before doing surfing

D．you must first swim to the swells with your board

在数据传输中，如不加（）控制，直接用信道来传输数据信号，一般来说传输质量是（）。

换热器日常维护的主要内容有（）。

A、检查换热器有无泄漏

B、检查换热器出入口压差

C、应注意换热器上的温度计准确可靠

D、换热器管束试漏