The correct answer is A. Simile
Step-by-step explanation:
The simile and metaphor are both figures of speech mainly used to make a comparison or create a relation between two elements or concepts, because of this, similes and metaphors are widely used in literary works and especially in poetry to create complex concepts or identify the similarities between two ideas. But despite simile and metaphor are similar, there is a difference between both, in the case of simile the relationship or similarity is established by using words such as "like", "as", "so" or any other that directly shows the relationship between the two elements or concepts being compared, on the opposite in metaphor these words are omitted. Considering this, in the case of the sentence "White as a white cow's milk" the figure of speech in this sentence is a simile considering two concepts (the white color and the cow's milk color) are being compared and the word "as" that establishes the relationship between both is used.