Read this sentence from paragraph 7. Researchers are especially interested in . . . periodical cicadas; these insects live only in this part of the world, and they appear just once every 17 years, on the dot. Why has the author chosen to use the figurative phrase on the dot?
A to describe the small holes made by cicadas as they hatch
B to highlight their specific and extraordinary life cycles
C to identify the precise location where they may be seen
D to suggest the amazing regularity of when they will emerge