Which of the following is a common mistake made in speech conclusions?

Introducing new ideas in a speech conclusion is indeed a common mistake. The conclusion should serve to reinforce the main points discussed throughout the speech and provide a sense of closure. When new ideas are introduced at this stage, it can confuse the audience and detract from the overall message. A conclusion should summarize the key takeaways, providing a cohesive wrap-up of what has been presented. This ensures that the audience leaves with a clear understanding of the topic and the speaker's main arguments.

In contrast, thanking the audience, summarizing main points, and asking listeners to take action are all effective techniques that can enhance a conclusion. Thanking the audience shows appreciation, summarizing reinforces the key messages, and a call to action can motivate the audience to engage further with the topic.