Final answer:
The metaphor in the given options is 'b. Life is like a box of chocolates,' as it directly compares life to a box of chocolates.
Step-by-step explanation:
The metaphor is a literary figure of speech that makes a direct comparison between two unlike things, implying they are one and the same without the use of like or as. In the given options, the metaphor is 'b. Life is like a box of chocolates,' as it directly compares life to a box of chocolates without using like or as. The other options use similes to make comparisons.