Answer:
c. take a long time deciding what your message will be
Explanation:
When called upon to give an impromptu speech, it is not a good idea to take a long time deciding what your message will be because impromptu means that you were called in the spur of the moment, so you can't take a lot of time as you will need to speak inmediately.
Also, start off strong and with confidence, decide on your transitions from one point to the other and maintain eye contact with the audience are things that you should do and that will help you to deliver the message appropiately to the audience.
