The correct answer here is C.
When they use "word music" poets try to make their poems sound musical. They try to use their words to imitate the actual sounds that are involved in "real" music.
If you look at the four options you gave, all but C would be useful in trying to accomplish this purpose.
Rhythm and meter are clearly connected to music since rhythm is such a big part of music and meter contributes to the rhythm of a poem.
Rhyme and repetition are conncted as well since lyrics often rhyme and rhyme and repetition can evoke the feel of a song's chorus.
Alliteration and assonance also create rhythm and rhymes.
On the other hand, similes and metaphors do not necessarily do anything for the sound of a poem. They do create images in the mind, but not through their sounds -- more through the words that are used.
In terms of the ideas presented, I would say that all of them have a place and meaning in the conception of music. I think that alliteration and assonance might not have as much sway in the construction of music. Indeed, the previous post's argument that similes and metaphors do not enhance the sound of the music is compelling. I guess I would argue that the rhyme and meter of a song could subsume if there is alliteration or assonance. At the same time, similes and metaphors not only enhance the meaning of the song, but would be able to have more of an impact on the creation and effectiveness of a song than the arrangements of consonants or vowels. I am not sure if there is a certain or exactly correct answer to this as much as there is an exploration of accurate answers that might be able to bring one closer to understand how music is created.
The term word music refers to words, either by themselves or read together that make sounds similar to those heard in music.
a) Rhythm and meter have the same meaning in words as they do in music: the variations of stressed and unstressed beats. here's an example of word rhythm/meter from Poe's "The Raven" showing stressed and unstressed syllables:
ONCE u PON a MID night DREAR y, WHILE i POND ered WEAK and WEARy
b) Rhyme is the repetition of certain sounds of the words, again from the same line of "The Raven," the rhymes are shown bold:
Once upon a midnight dreary, while I pondered, weak and weary
Repetition is repeating of word phrases or single words:
As of some one gently rapping, rapping at my chamber door...
d) Alliteration is the repition of consonant sounds:
Once upon a midnight dreary, while I pondered, weak and weary,
Assonance is repition of vowel sounds:
But the silence was unbrOken, and stillness gave nO tOken,
and the Only word there spoken was the whispered word,
And so the devices that are not word music are: c) simile and metaphor. Neither of these devices relies on sound. They rely on comparisons of meaning. "His hair was like steel wool" is a simile. "The old ship was a was a bucket of rust" is a metaphor. No music is needed for them.