Answer: Option D
Explanation: First, we should try to eliminate options that we know are incorrect to make it easier to find the answer. We can eliminate A because three can't go into 20. We can also eliminate option C because five cannot go into 12. That leaves us with B and D. 3 can go into 12, and 2 can go into 20, but let's review both options before we make a choice.
12 divided by 20 (the ratio of parrots to birds at the pet store) = 0.6
Three divided by 2 (option B, a possible equivalent ratio) = 1.5
12 divided by 20 (the ratio of parrots to birds at the pet store) = 0.6
Three divided by 5 (option D, a possible equivalent ratio) = 0.6
Option D's ratio is equivalent to the ratio of parrots to birds at the pet store. Therefore, pick 3 to 5.