The reason why the structure of the statement is reversed is to draw attention best to the "time" of the spring comes, rather the "action" of it. That is why the adverb "presto" is at the beginning and the noun is at the end. If to put them in an evaluating order, it would like:
"presto" > "arriva" > "la primavera" (as the structure itself suggested")
Another example could be like; "La pasta mi piace molto" (emphasizing the noun, rather than the action here: "I like pasta very much rather than the other food)
"Mi piace la pasta" (more general and more common, emphasizing nothing particular: "I like pasta")
I had the same hesitation, more frankly, mistake but there is a slight, yet important difference between "soon" and "early" in English. In a general sense, the adverb "early" gives the meaning "happening or done before the usual or expected time" or "belonging or happening near the beginning of a particular period" (Oxford Dict.). However, the adverb "soon" has a slightly optimistic/positive/less hesitant significance which means "in or after a short time" (Oxford Dict.)
Example: The train arrived early. (The train arrived at a time that I wasn't expecting it to arrive)
The train arrived soon. (The train arrived at a time to which I gave a thought.)
I hope this helps a bit.
I think you will need to deduce the meaning intended from the context, you know, because as you will see in this link, there are many slight but important changes of meaning within just one word. Yet, I suppose, if it is really meant something like "earlier than expected and than it is supposed to be" etc., then perhaps it could be written as "in anticipo."
Spring arrives soon and spring arrives early mean two different things. That said, "presto" means both "early" and "soon" so I am not sure why "Spring arrives early" would not be marked correct since there is no context given. I wrote the sentence using "early" and was marked incorrect. Confused.
Wrong sentence construction? Really? In what way? And how does Emily's sentence construction of "The Spring soon arrives" differ from "Spring is arriving soon", which DL gives as a correct answer? Only in the adverbial position at the end in DL's version. It can be argued that DL did so to give emphasis to "soon". But what in the context warrants such emphasis? DL rejected "Spring soon arrives", but there is no semantic difference from "Spring is arriving soon" and no contextual difference to warrant its accepting the latter and rejecting the former. When two English translations have the same meaning, they should both be accepted or both be rejected, unless the objective of this course of study is to teach "emphasis".