【正确答案】 B

【答案解析】[听力原文]
Today we are going to practice evaluating a main tool used when addressing groups—the voice. There are three main elements that combine to create either a positive or negative experience for listeners. They can result in a voice that is pleasing to listen to and can be used effectively. Or they can create a voice that doesn"t hold attention. The three elements are volume, pitch and pace.
When evaluating volume, keep in mind that a good speaker will adjust to the size of both the room and the audience. Of course, with an amplifying device like a microphone, the speaker can use a natural tone. But speakers should not be dependent on microphones. A good speaker can speak loudly without shouting.
The second element, pitch, is related to the highness or lowness of the sounds. High pitches are for most people more difficult to listen to. So, in general, speakers should use the lower registers of their voice. During a presentation, it"s important to vary pitch to some extent in order to maintain interest.
The third element, pace—that is how fast or slow words and sounds are pronounced—should also be varied. A slower pace can be used to emphasize important points. Note that the time spent not speaking can be meaningful too. Pauses ought to be used to signal transitions or create anticipation . Because a pause gives the listener time to think about what was just said or even to predict what might come next. It can be very effective when moving from one topic to another.

What is the main point the lecturer makes?

[解析] 比较四个选项大致可以推测本题问的是本文的主要内容。
短文开头即说明了短文的主要内容：评价演讲时最主要的工具——声音，并分三个要素加以分析，脉络很清晰。因此答案为B。

【正确答案】 A

【答案解析】[听力原文]
According to the lecturer, how can a speaker indicate that the topic is about to change?

[解析] 四项都是以by开头的短语，考查的是做事方式。
短文中的signal transitions与问题中的indicate that the topic is about to change同义，并且短文最后两句还对停顿(pause)为什么有用做出了解释，因此答案为A。