Why are some polymers elastic?

Releasing the stress allows the kinks, coils and loops to form again, and the rubber returns to its original dimensions. Materials made of long, tangled molecules stretch very easily. Their elastic modulus is very small. They are called elastomers because they are very "elastic" polymers

Polymers are elastic because their strength of recovering their original shape is high having very weak inter-molecular forces and low Young's modulus

Polymer chains are held together in polymers which are elastic materials by very weak intermolecular bonds, which aloow the polymers to stretch in response to macroscopic stresses applied to them. This extreme flexibility in elastic polymers can extend from 5–700%, depending on the specific material. This elasticity is not due to covalent cross-links, but instead for thermodynamic reasons. So we can say that polymers are elastic because they have very weak inter-molecular forces and low Young's modulus.

the correct answer is: b. pantala flavescens, because these organisms would have a high level of genetic variation due to sexual reproduction.  

because involves two organisms (parents) whose genetic material combines, sexual reproduction leads to genetic variation in new generations of offspring. the offspring is an unique organism, with new genome, more protected with the higher ability to adapted. this process is fundamental to evolution.