Which of the following is the best method for achieving an informal style in a speech?

Using contractions is indeed a highly effective method for achieving an informal style in a speech. Contractions, such as "can't," "won't," or "it's," help create a conversational tone that can engage listeners and make the speaker appear more relatable. This approach mirrors everyday spoken language, which typically incorporates contractions, thus enhancing the natural flow of the speech and making it more accessible.

While slang can also contribute to an informal style, it may risk alienating or confusing some audience members, especially if the slang terms are not universally understood. Defining technical terms is essential for clarity in more formal communication and doesn’t necessarily promote an informal style. Including hypothetical examples can be effective in illustrating points, but it doesn't inherently contribute to making the speech feel informal. Contractions, on the other hand, create an immediate sense of informality and connection with the audience, making them the best choice for achieving an informal style.