**Core Concept**
The girl's behavior is indicative of a developmental disorder characterized by a lack of social interaction, delayed or absent language development, and restricted interests. This condition is associated with abnormalities in social communication and interaction.

**Why the Correct Answer is Right**
The girl's behavior is suggestive of Autism Spectrum Disorder (ASD), which is characterized by difficulties in social communication and interaction, alongside restricted and repetitive patterns of behavior. The repetitive behavior of focusing on her own hand and lack of interaction with others are classic signs of ASD. The diagnosis of ASD is made based on clinical evaluation, including observations of behavior and developmental history.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the girl's behavior does not suggest a primary motor or sensory disorder, which would be characterized by significant delays in gross motor skills or sensory processing difficulties.

**Option B:** This option is incorrect because the girl's behavior does not suggest a primary anxiety disorder, which would be characterized by excessive fear or anxiety in response to specific situations or objects.

**Option C:** This option is incorrect because the girl's behavior does not suggest a primary attention-deficit/hyperactivity disorder (ADHD), which would be characterized by symptoms of inattention, hyperactivity, and impulsivity.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that early diagnosis and intervention are critical in autism spectrum disorder, as they can significantly impact the child's developmental trajectory and quality of life.

**Correct Answer: C.** Autism Spectrum Disorder