Answer:
common themes
Step-by-step explanation:
The answer in the blank, I believe is common themes. It is because using common themes or including them on the speaker's speech could make the audience relate on the topic and to be intrigued or to be interested. With this method, not only will the speaker give out his information but he or she could capture the attention of the audience.
Moreover, the answer could be allusions which are references to a well-known person, character, place, or event. But, for the most part I believe the answer to be common themes, and allusions could work too.