An example would be.

This one is harder to tell
A) complete sentence
B) fragment
C) run-on
I want to say it is b a fragment..

Yes, it's a fragment.

Is it because it doesn't have much detail?

There needs to be a subject complement after would be.

To determine whether the given statement is a complete sentence, a fragment, or a run-on, we need to understand the characteristics of each type:

A complete sentence:
- A complete sentence expresses a complete thought.
- It contains both a subject (the main noun or pronoun) and a predicate (the verb or verb phrase that tells something about the subject).
- It can stand alone and make sense on its own.

A fragment:
- A fragment is an incomplete sentence.
- It is missing either a subject or a predicate or both.
- It cannot stand alone and does not express a complete thought.

A run-on:
- A run-on occurs when two or more independent clauses are joined together without proper punctuation or conjunctions.
- It is often a long sentence that lacks proper structure, making it difficult to follow.

Now, let's apply this understanding to your statement: "This one is harder to tell."

- The statement has a subject ("This one") and a predicate ("is harder to tell").
- It expresses a complete thought.
- It can stand alone and make sense on its own.

Based on these observations, the given statement is indeed a complete sentence. Therefore, the correct answer is not B) a fragment, but A) a complete sentence.