In any sentence, there is always a subject though sometimes the object is not included. The subject in any sentence is the one doing the action/ verb or who/ what the verb is based on. So, the subject in the sentence is the "water" which 'leaped'.
In the sentence,
The water <em>leapt</em> up from the center of the <u>spring</u>
the water is the subject, leapt is the verb which describes the action of the water and the spring is the object.
I might be wrong but i think its a fragment sentence to be sure look up the definition of the answer choices that sometimes help me figure out the answer.
