The answer is a. In order to make sure that audiences can correctly hear all the syllables of the words you are speaking, it is necesarry to make sure you have a correct enunciation.
The enunciation is the act of pronouncing words clearly and articulate, pronouncing all the syllables in every word.
Intonation is also necessary when speaking clearly, but in this case, it helps distinguish punctuation marks, for example, if a sentence is a statement or a question. Elucidation, on the other hand, refers to the act of explaining something or making it clear, in this case it refers to the meaning of the words.