Which of the following examples would be a good example of coevolution?

Coevolution and Pollination - WNPS Blog - Botanical Rambles

a
The long narrow bill of a hummingbird and a tube shaped flower.
b
The teeth of a lion and the claws of a cheetah.
c
Brothers competing for the same date.
d
Two species of birds that both use the same resources.

a

The long narrow bill of a hummingbird and a tube shaped flower.

This is a good example of coevolution because the shape of the hummingbird's bill has evolved to match the shape of the flower, allowing the hummingbird to efficiently extract nectar from the flower while pollinating it in the process. This mutually beneficial relationship shows how the traits of both the hummingbird and the flower have evolved together over time.