A 16- year- old boy presents to his high school counselor after running out of his programming class b/c he was asked to explain a piece of code. He has trouble answering and had felt this sort of difficulty in the past, but today it was worse. He is not able to explain clearly to the counselor what happened b/c he is still having the same speaking problems that he has in class. He speaks in broken words and keeps getting stuck on sounds like "aye" and "ah". He seems to spit out words. He writes down on a piece of paper that he has been thinking about dropping out of school b/c of his difficulty speaking; his older brother dropped out of school for similar problems. The counselor later observes him working in the computer lab and notices no abnormal behavior. What is the likely diagnosis?

A Autism spectrum disorder.
B. Childhood- onset fluency disorder (stuttering).
C. Social anxiety disorder (social phobia).
D. Tourette's disorder.