Which is a scientific question? Can cats learn to sit down on command? Why do black cats bring bad luck? Are spotted cats cuter than solid-colored cats? Why are Persian cats so funny?

The scientific question among the options provided is: "Can cats learn to sit down on command?" This question can be tested through experiments and observations, and it seeks to understand a specific behavior of cats that can be measured and analyzed. The other questions are based on subjective opinions or cultural beliefs and cannot be tested scientifically.