When Jackson Sees That His Audience's Attention Is Lagging a Bit

When Jackson sees that his audience's attention is lagging a bit, he raises the intensity and volume of his voice to emphasize a series of points. Jackson then lowers his volume a bit to a more comfortable level for the audience, but occasionally accentuates important information in the same way. In response to his audience, Jackson is adjusting which aspect of his vocal delivery?

A) rate
B) force
C) articulation
D) pronunciation