Which of the following manner of articulation is NOT characterized by a complete closure of the vocal tract?

The manner of articulation that is characterized by not having a complete closure of the vocal tract is nasal. In nasal sounds, the airflow is directed through the nasal cavity while the oral cavity is typically closed; this allows for resonance in the nasal passages.

In contrast, stops involve a complete closure of the vocal tract, creating a build-up of air pressure that is released suddenly. Fricatives are produced by forcing air through a narrow channel, resulting in turbulent airflow, which means there’s no complete closure, but there is a significant constriction. Affricates begin as stops, where there is complete closure, followed by a release that creates a fricative sound; hence, they also start with a complete closure.

Thus, among the given options, nasal sounds are the only category where the articulation does not involve a complete closure of the vocal tract, affirming that "B" is the correct choice.