Final answer:
The range of motion of the oral structures has a significant effect on utterance length because it determines the articulation of sounds; limited motion can lead to shorter utterances.
Step-by-step explanation:
The factor which has a significant effect on utterance length from the options provided is a. Range of motion of the oral structures. Human speech production involves the shaping of the cavity formed by the throat and mouth, as well as the vibration of the vocal cords. The tongue plays a crucial role in adjusting the fundamental frequency and combination of overtones. Oral structures, including the tongue, lips, jaw, and palate, determine the articulation of sounds. If there is a limited range of motion in these structures, it can result in reduced utterance length because the articulation of certain sounds, particularly consonants that require more precise movements, would be restricted.
Other factors in the list, such as pharyngeal fricatives, nasal emission, weak consonants, and hypernasal resonance, may affect speech quality, but they do not significantly affect the length of an utterance in the same way that the range of motion of oral structures does.