Which is a sentence fragment?
A. Because I spent three hours on my homework.
B. I'll probably find it somewhere in my backpack.
C. The assignment disappeared off my hard drive.
D. I am frustrated so I deleted the entire thing.
The answer is A. Because I spent three hours on my homework.
This fragment provides a verb statement, but there is no subject preceding this statement. A sentence must have a subject-verb agreement to be considered a sentence. Without one or the other, it is a sentence fragment.