Which of the following is a common sign of ASD?

A common sign of Autism Spectrum Disorder (ASD) is avoidance of eye contact, as individuals with ASD often struggle with social interactions and may have difficulty with nonverbal communication cues. Eye contact is a significant aspect of social engagement and communication, and those on the spectrum may find it uncomfortable or challenging, leading to the tendency to avoid it. This behavior can be a reflection of a broader challenge with social reciprocity that is characteristic of ASD.

In contrast, excessive talking and a highly social demeanor are not typical signs of ASD. While some individuals with ASD may have extensive knowledge or interests in specific topics that lead to them talking about those subjects a lot, it doesn't mean they are socially engaged in the same way as their peers. A highly social demeanor would suggest comfort in social situations, which is generally not the case for many on the spectrum.

Strong emotional responses might occur in individuals with ASD, but they can also be challenging for them in terms of emotional regulation, often leading to difficulties rather than just strong expressions of emotion. Therefore, avoidance of eye contact is the most identifiable and common sign related to ASD among the options presented.