Honestly all these options are components of oral communication. But the most essential two components of oral communication are:
C: Pitch and eye contact
and
D: Proper volume and facial expressions.
Because when you think about it, accents and speaking disabilities (option A) can render enunciation and speaking rate. So although someone's enunciation and speaking rate can be a components of oral communication, it's not the main two that we are looking for.
As for B: Eye contact and pronunciation, people speak to one another on the phone and/or text all the time. So eye contact isn't the<em> most</em> necessary. As for pronunciation, it's essential, but not part of the top two. I'd say that pitch is more important (in option C) because for example, when people ask a question the pitch goes up at the end of the sentence. This is a clear indicator.
