Final answer:
In ASL, eyebrows and facial expressions frequently act as grammatical markers, indicating questions, the tone of the statements, and the intent behind signs.
Step-by-step explanation:
In American Sign Language (ASL), the facial feature that often functions as a grammatical marker is the eyebrows and other facial expressions. In ASL, a signer will use facial expressions to indicate a variety of grammatical constructs, such as raising the eyebrows to signal a yes/no question or furrowing them for a WH-question. Facial expressions in ASL play a significant role in conveying the nuance and intent behind signs and often act much like intonation does in spoken languages. This aspect is crucial in ASL as it adds depth to communication and helps to differentiate between statement, question, and command forms.