Answer:
Option C
Explanation:
While giving a public speech/talk, it is not advisable to see at one particular person in the audience as it leads to disinterest among the others.
Hence, option A is incorrect.
Referring to notes too make the audience distracted. Hence, option B is incorrect
Speaker must be able to speak clearly so that everyone understands what he/she wants to convey. Clear vocals are a plus for good talk delivery. Hence, option C is correct.
Option D and E seems to be inadequate as a friend on stage will not make speech/talk interesting untill unless the speaker do something on his own. Also, memorizing every word is not a solution. Sometimes people who memorizes speech/talk content get nervous on stage when they forget even a single line.