Final answer:
The sentence is a fragment and lacks a main clause to be complete. Fragments, such as 'A flash of movement,' require additional parts to form a complete thought. To fix a fragment, you add what is missing or combine it with another sentence.
Step-by-step explanation:
The sentence 'When we adopted the cutest puppy at the animal shelter.' is a fragment because it lacks a complete thought and doesn't have a main clause. A complete sentence needs at least a subject and a predicate that express a complete thought. In this case, the sentence seems to need an additional part, such as what happened when the puppy was adopted. For example, 'When we adopted the cutest puppy at the animal shelter, our family was overjoyed.' This new sentence provides a complete idea.
A sentence fragment is similar to what you see in this example: 'The rabbit darted out of the shadows. A flash of movement.' Here, 'A flash of movement.' is a fragment. It can't stand alone as a complete sentence because it lacks a subject and verb. Conversely, a comma splice is when two independent clauses are joined incorrectly with only a comma. For instance, 'The dog lunged and strained at the leash, comma splices are grammatical errors.' should be separated into two sentences or joined with a conjunction or semi-colon.
To complete or fix a fragment, we need to add the necessary elements that are missing or join it to another sentence. Consider this correct sentence: 'When a stray cat came to our back porch and my daughter wanted to keep it, he changed the rule about "No Pets."' It has a clear subject, 'he,' and a complete predicate, 'changed the rule about "No Pets."'