Answer: B. Written comments on evaluation forms.
Explanation: In order for us to arrive at our answer, we must enable ourselves to review each individual option.
A. "One-on-one conversations between the speaker and each audience member." While the notion of receiving feedback is present, the concept of having a one-on-one conversation with every audience member is very ineffective, and may take significantly longer than the actual speech itself.
B. "Written comments on evaluation forms." Such a practice allows the audience members to provide constructive criticism as the speaker presents their ideas and of course, themself. Due to the nature of this selection, it provides both the speaker and the audience to engage in other activities after the speech, such as a Q&A.
C. "A Q&A session at the end of the speech." While a questioning and answering session may provide some constructive criticism and evaluations, it is not the sole purpose of such an activity. The Q&A can range from generalized or specific questions the audience has, that may not necessarily degrade or improve the work of the speaker themself.
D. "An oral evaluation delivered to the speaker by one delegated audience member." While the notion of an evaluation is present in this specific answer, it being conducted by only one delegated audience member may not only be open to biases, but also prove itself ineffective as one audience member can not speak on the behalf of the entire audience, and not to mention, there may be opposing views that the audience member does not address.
After reviewing these answers, we can select that the best answer would have to be: B. "Written comments on evaluation forms."