Answer:
What is the smallest bridge in the world?
By Moon or by Sun, I shall be found. Yet I am undone, if there's no light around
I am the tool, for inspiring many. Buy me in the store, for not much more than a penny. Don't overuse me, or my usefulness will go.
Give it food and it will live, give it water and it will die.
A seed am I, three letters make my name. Take away two and I still sound the same.
People take me on walks and I run and have fun. What am I?