The linking verb is "could have"
Tone, as you may know, is the general attitude an author takes in the construction of a story, essay, poem, etc. that can be determined by the author's choice of words. When we look at the essay, "Murmurs," by K.C. Cole, we see slang/informality in the author's word choice in the following sentence from the essay: "Because there's scientific gold in them there sinusoidal
hills." Additionally, there are many analogies and similes the author uses in the explanation of concepts such as when the author writes "Like children going after cookies the patterns of sloshing particles left their sticky fingerprints all over the sky." As such, one way to describe the author's tone would be informal (almost playful/humorous) yet informative.
