I believe the answer is B. Structural adaptations are characteristics that change over time. Some animals adjust over the years to live better in their environments, and this is what it was talking about.
Elephants have long trunks to reach leaves they couldn't get to if their trunks were small. Same with the humming bird and the rose bush. They are adapting. However, the dog is only getting a drink. The dog can do that without having to adapt to anything.
