Which sentence is the best example of metaphor?

a. "watch out! " walter cried, waving his arms frantically.
b. in the 105-degree weather, the city became a vast microwave oven.
c. gold, orange, red: the leaves showed all the colors of autumn as we drove.
d. ripples spread out from the point where the stone had been cast into the pond.

The answer is B: In the 105-degree weather, the city became a vast microwave oven.

A metaphor is a figure of speech that establishes a comparison or analogy between two things by referring to one thing but mentioning another. A metaphor tends to bring out the identity or similarity between two ideas that would be, in literal terms, disassociated otherwise.

A metaphor is different than a simile in as much as a metaphor directly establishes the similarity or comparison between two things (“the city became a vast microwave oven), whereas the simile does this in an indirect way, by introducing the word “like” or “as” (for example: the city was like a vast microwave).  

1.the hosts on two opposing mountains stood,  

2.thick as the foliage of the waving wood;  

3.between them an extensive valley lay,  

4.o'er which the gleaming armour pour'd the day,  

5.when from the camp of the philistine foes,

6. dreadful to view, a mighty warrior rose; in the dire deeds of bleeding battle skill'd,