Answer: C. Rich people have a better appreciation for life when they become poor.
Explanation:
The Mexican proverb "The rich person is richer when he becomes poor, than the poor person when he becomes rich." simply means that "Rich people have a better appreciation for life when they become poor".
When a rich person becomes poor, the person sees life differently and appreciates life more they become poor unlike the poor man who hasn't witnessed wealth before. Therefore, the correct option is C.