Answer:
The insects.
Step-by-step explanation:
Insects would be the organisms most likely to survive a bombardment or the impact of comets and asteroids. This is not due to the insects' body structure and composition, but because of their habits.
All insects have an exoskeleton formed by chitin. This subtlety does not promote resistance to chemicals and impacts as strong as that caused by asteroids and bombs. However, some insects have a habit of always hiding themselves in cracks in the walls, in drains, under objects etc. This ability is what would promote the survival of some insects. This is because, once "protected" they would have a better chance of surviving than the organisms that live on the surface of the earth, such as mammals.