Asteroids vary greatly in size and are mostly made up of frozen water and gas. This one is true.
They are said to be "mostly formed of ice and gas" as they rarely can be found consisting of stone, nickel and iron. These are extremely dangerous in our Universe.
They use their resources and habitats around them to survive.
Answer:
A) Agents
Hope that helped! I wasn't 100% sure but I hope this is right. If it's wrong, please tell me! Have a good day!
I believe they use enzymes