The correct option is B Metaphor
'Metaphor' is a literary device / figure of speech in which a word or a phrase is given / applied to an action, object or event where it is not literally applicable. In simpler terms, a metaphor is a comparison that is drawn between two completely unrelated things. In this case, the class has been compared to a dessert due to it being something that the speaker looks forward to and enjoys; and something that comes at the end of the 'meal' that is the whole day, which cannot be literally true. Thus, the correct answer is Option B) - Metaphor. All the remaining options are also literary devices, but they have not been used in the given sentence.