How are fricative sounds characterized?

Fricative sounds are characterized by their production involving continuous airflow through a narrow constriction in the vocal tract, which creates turbulence and a characteristic sound. This definition aligns directly with the idea of "use of airflow without blockage." In contrast to other sounds, like stops, which involve complete closure of the vocal tract, fricatives maintain an open channel allowing air to flow, resulting in a hissing or buzzing quality.

The presence or absence of vocal cord vibrations is not a defining characteristic exclusive to fricatives—both voiced and voiceless fricatives exist, making option C less specific. While fricatives do involve articulation at specific places in the mouth, this characteristic relates more broadly to the formation of various consonant sounds rather than defining them as fricatives, which makes option D not as precisely tailored to the question. Therefore, the first choice best encapsulates the defining feature of fricatives in phonetics.