If the options are metaphor, alliteration, allusion, and apostrophe, I believe the answer is metaphor, because the others don't fit.
Alliteration is the repetition of a consonant.
Allusion is reference to something or somebody outside of that literary work.
And apostrophe is the author speaking directly to somebody outside the poem, usually gods or a muse.
An improper grammer sentence.
<span>The tone of the letter is too informal and lacks details needed for a good resolution.
Hope this helps! Please let me know if I'm wrong :)</span>