The correct answer is A.
Here, the author deduces that, if a person wants to adopt a dog, it is important that he does not get just any dog. He should investigate what type of dog would suit his lifestyle better, for not all dogs can live in all spaces.
For example, if he lives in an appartment, he should not get a big dog that would need a great amount of space to run and excercise. He should probably get a small or even medium dog that would live there more comfortably.