Answer: by varying the tone and volume of his voice
Explanation: Victor should improve his presentation by varying the tone and volume of his voice (option B). This technique can help maintain the audience's interest and engagement.
By modulating his voice, Victor can emphasize key points, add enthusiasm and energy to his delivery, and create a more dynamic and captivating presentation. This approach is more likely to grab the audience's attention and keep them engaged compared to the other options suggested. Laughing loudly, shouting, or displaying annoyance through frowning are not clear strategies for maintaining audience interest, and may even have a negative outlook on their reactiveness to the presentation.