Assonance is the repetition of the same vowel sound within a group of words. For instance, refer to "May was late today." In this example, the "a" SOUND is the same in "May," "late," and "today." Remember, it is not the same letter that creates the assonance, but the sound. As another example, "neighbor," "grace," and "save" are ALL examples of assonance because in all three words, the "a" (though written as "ei" in "neighbor") creates the SAME SOUND.
Consonance is much the same, except it concentrates on consonant SOUNDS within a group of words. For example, in "Dennis went to town," consonance applies because the SOUND is the same in three of the words: the "n" sounds the same in "Dennis," "went," and "town." It does not matter that the sounds are found in different places within the three words.
The only things you cannot do in creating consonance are: do not place one of the letters at the beginning of a word. (Repetitive consonant sounds at the beginning of words is called "alliteration," and cannot be mixed with consonance.) Secondly, if an "n" is used that is part of a "consonant blend" that creates a different SOUND, it cannot be used. For example, "bank" does not have the same sound as "went." Let your ears guide you, not your eyes.
True rhyme is when words sound exactly the same. "Fame" and "game" create true rhyme, but "done" and "when" do NOT create true rhyme. They are used as "near rhyme," which is something poets will often do. For example, Shakespeare's Sonnet 29 (a great love poem) uses a rhyme between "possess'd (a contraction of "possessed") and "least." They sound very similar, but are not the same.
In answer to your question, then, I find the choices provide only one correct answer. With 'em and livin', the last letters of the words are not the same—different sounds mean consonance is not used.
Because the sounds are not the same, I would identify the words as "near rhyme," not "true rhyme." The consonants used have different sounds, and the vowels, which generally carry the rhyme, also have a different sound.
In terms of assonance, you should select that answer "a"), as the vowels used create the same sound, according to Bedfords/St. Martins:
...Assonance occurs when the vowel sound within a word matches the same sound in a nearby word...
Bedfords/St. Martins also gives a more in-depth example:
...the repetition of internal vowel sounds in nearby words...for example, "asleep under a tree," or "each evening."
According to this source, vowels sounds can be found within words or at the beginning of words. In other words, if the repeated sounds are found—with vowels—within the word or at the beginning of words, assonance exists if the sounds are the same.