阅读理解。
Although there are many ways in which people communicate through speech, public speaking
has probably received more study and attracted more attention than any other. Politicians winning
an election, salespeople presenting products and etc. All depend upon this form of public
communication. Even people who do not make speaking a part of their daily work are often asked
to make public speeches: students at graduation, for instance, or members of churches, clubs or
other organizations. Nearly everyone speaks in public at some time or other, and those who perform
the task well often become leaders.
There are many reasons for speaking in public. A public speaker may hope to teach an audience
about new ideas, or provide information about some topic. Creating a good feeling or entertaining
an audience may be another purpose. Public speakers, however, most often seek to persuade an
audience to accept new opinions, to take certain actions, or to see the world in a new way.
Public speakers usually know well in advance when they are scheduled to make a speech.
Consequently, they are able to prepare their message before they deliver it. Sometimes, though,
speakers must deliver the message unprepared, or off the cuff, such as when they are asked to
speak at a wedding reception or to participate in an interview.
When they do not have to speak unprepared, most speakers write their own speeches. Politicians
and business managers sometimes employ professional writers who prepare their speeches for them.
These professional writers may work alone or in small teams. Although the speaker may have some
ideas into the contents of the speech, the writers sometimes have a great influence over the opinions
expressed by their employers. Regardless of how a speech is prepared, the person who delivers it is
given credit for its effect upon its hearers.
1．Public speaking is well known to average people because ________.
A. most of them have been trained as public speakers
B. most of them have been audience of such activities
C. most of them have to do it when they study at college
D. the passage does not mention the reason
2．Which of the following is rarely the purpose of public speaking?
A. To influence people's ideas and behaviour.
B. To persuade the audience to accept an idea.
C. To enjoy the satisfaction from one's own speech.
D. To develop public interest.
3．No matter who writes a speech, the audience ________.
A. do not believe what the speaker says
B. know very well whom the speaker is
C. know whose idea the speech really expresses
D. believe it expresses the speaker's idea
C+D，若t1时增大压强，正、逆反应速率变化如图所示（ν代表反应速率，t代表时间），下列有关A、B、C、D的状态叙述中正确的是 
