Answer:
The option that is not a purpose of transitions is:
b. introduction sub points.
Transitions primarily serve to improve the "flow" of the speech and establish connections between ideas, and they may include references back to the speech. However, the specific purpose of introducing subpoints would generally be achieved through the structure of the speech itself, rather than through transitions. Transitions are more about guiding the audience smoothly from one point or idea to the next.
Step-by-step explanation: