A metaphor is a form of comparison without using the words such as "like" or "as," because that would be a simile. This means that C and D are incorrect, because those are examples of a simile, not a metaphor. In B, nothing is being compared, so that option is also incorrect. Thus, the correct answer is A, where "hooves of rain" is a metaphor - horses don't really have hooves made of rain, but somehow resembling rain.
