Issues with explanation for why A is wrong

Hi @miabartolomei, Thanks for the question! I wouldn’t say that the issue with (A) has to do with the fact that dogs scratch themselves out of convenience. That was probably just put in there a side note or maybe something for fun. The reason (A) is wrong is because it doesn’t tell us anything about the relative frequencies about scratching with the left vs. right leg. So sure, maybe they scratch themselves with both. But if they usually scratch themselves with the right leg, that would suggest that they’re right-handed. (A) doesn’t say otherwise, so we can’t assume that it means that they scratch themselves equally. As to your broader point, there’s no bright line distinction. However, a general rule is that if it is “common knowledge” or “obvious,” it’s reasonable for the test takers to expect you to use that kind of knowledge. That would be as opposed to some kind of specialized knowledge, like something you would learn in an advanced psychology or biology course. Hope this helps! Feel free to ask any other questions that you might have.