The author's use of the oxymoron "awful harmony" in the passage from "Young Goodman Brown" suggests: d. The voices sing together, but the effect on Goodman Brown is frightful.
In this context, "awful" is not used to convey a sense of admiration or beauty, but rather to imply something dreadful, terrible, or frightening. The harmony of the sounds in the wilderness creates a chilling and unsettling atmosphere for Goodman Brown, contributing to the ominous tone of the story.
The author's use of the oxymoron "awful harmony" in the passage from "Young Goodman Brown" suggests the voices sing together, but the effect on Goodman Brown is frightful.