What essential component must be present in a syllable?

A syllable is a fundamental unit of sound in language, and it must contain a vowel sound to be considered complete. The presence of a vowel is what distinguishes a syllable from other sounds and structures in language. Every syllable has at least one vowel, which can stand alone or be accompanied by consonants before or after it. This is why the correct answer is that a vowel is an essential component of a syllable.

In contrast, while a consonant may accompany the vowel in many syllables, it is not a mandatory component. A syllable may consist of just a single vowel sound, such as "a" or "I." Similarly, a diphthong, which is a complex vowel sound formed by the combination of two vowel sounds, is also not required for a syllable's existence. Lastly, a pause is not a structural component of a syllable; rather, it can influence rhythm and meaning in speech but does not define the syllable itself.