Which question could not be answered by using the scientific method?

do black cats eat more than white cats?
what am i thinking right now?
which has more calories, soda or milk?
why does the tide change during the day?

For the first question you could devise a way to test the question to find the answer. You could create a sample of black cats, a sample of white cats, and a control sample of a both black and white cats. 
You would measure how much the cats eat each day. The study could be repeated or reviewed by your peers. 

For the second question, there is currently no way to sample a person's thoughts, but even if there was a way, there would be no way to repeat the moment. It is not testable and not repeatable and thus cannot use the scientific method. 

Calories can be measured and compared. 

The tide can be observed until someone hypothesizes the right testable notion to determine the answer.