The correct answer is D.
Decasyllabic means consisting of or containing ten syllables.
A syllable is a group or a unit of a speech sounds. They are the building blocks of words. A word consisting of a single syllable is called monosyllable, dissyllable means consisting of two syllables, and trisyllable of three etc.
In the above example, only the fourth example is decasyllabic, the first one has seven syllables, the second fourteen, the third thirteen.