Ellen noticed that she often sneezes when she visits her friend Robert, who has a cat and a parrot. Ellen wonders if she may have allergies to Robert's pets and decides to conduct a scientific investigation. What should Ellen do next

Ellen should visit a friend who has only cats and one who has only parrots.

Explanation:

Here is the complete question:.

Ellen noticed that she often sneezes when she visits her friend Robert, who has a cat and a parrot. Ellen wonders if she may have allergies to Robert's pets and decides to conduct a scientific investigation. What should Ellen do next?

A. Ellen should tell Robert that she cannot visit him until he gives away his pets.

B. Ellen should visit Sue who has a horse, a dog, a goldfish, and a hamster.

C. Ellen should call her doctor and insist that she needs shots for allergies.

D. Ellen should visit a friend who has only cats and one who has only parrots.

And the answer is

D. Ellen should visit a friend who has only cats and one who has only parrots.

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.