To hold on to something you have rather than take this risk to get something else that is just plain useless.
Explanation:
The proverb A bird in the hand is worth two in the bush' means that it's better to hold onto something you have rather than take the risk of getting something better which may come to nothing.
The correct option is D. The statement in option D reveals that the youthfulness which the four old people gained was very momentarily, it soon passed away and they were back to square one.
