Which word contains a diphthong?

The word "boiled" contains a diphthong, which is a complex vowel sound that begins with one vowel sound and glides into another within the same syllable. In "boiled," the vowel combination "oi" creates this glide, producing the sound heard in the word.

This characteristic sets it apart from the other choices. In "anchor," the vowels do not form a diphthong; instead, they are more distinct sounds. "Measure" contains a vowel sound, but it does not involve a glide between two vowels, making it a single pure vowel sound. "Truths" also lacks a diphthong, as the "u" sound does not transition into another vowel sound in a single syllable.

Thus, "boiled" is the correct choice since it uniquely features a diphthong with its vowel interplay, demonstrating a critical aspect of phonetics that is essential in language development and early literacy education.