Answer: The correct option is
E. a woodpecker using his sharp beak
Step-by-step explanation:
This is because a structural adaptations refer to characteristics or traits that animals possess and they use in order to adapt or survive in their environment. These refer to the physical characteristics of the animals.
From the question, a wood pecker using a sharp beak is an example of structural because the beak is the characteristics the wood pecker is using to survive in it's environment.