Which explanation fits with the concept of diphthongs?

The concept of diphthongs is best described as two vowels creating one sound. A diphthong is a complex vowel sound that begins with one vowel sound and glides into another within the same syllable, producing a blend that sounds distinct from each individual vowel. For example, the sound /oi/ in "coin" combines the sounds of the vowels 'o' and 'i' into a single, seamless sound. This characteristic is what differentiates diphthongs from other vowel sounds or combinations, which may involve a more straightforward pronunciation of individual vowels or a mix with consonants.

In contrast, other options describe different types of phonetic sounds that do not align with the definition of diphthongs. One long vowel sound suggests a monophthong, which is a single, pure vowel sound. A vowel and a consonant blend refers to a different structure where a vowel pairs with a consonant rather than creating the unique combined sound characteristic of diphthongs. Lastly, two vowels leading to a consonant sound does not capture the essence of a diphthong, as it implies an outcome that ends with a consonant rather than a combined vowel sound within a single syllable.