Answer:
C. The metaphor comparing Spot to lighting suggests that he is fast.
Explanation:
Both the metaphor and simile are figures of speech used to compare two things. The difference between them is the wording. The simile uses words like and as (e.g. Life is like a box of chocolates), while the metaphor omits these words (e.g. The curtain of night fell upon us).
Based on this, we can conclude that a bolt of lightning flashing is a metaphor. When someone or something is really fast, we often compare them with lightning or say that they are lightning fast. This means that Spot is very fast, which is why option C is the correct one.