Biology12 Identifying Carbohydrates help?

There was an experiment done to identify sugars using benedict's solution. We used water, glucose, fructose,sucrose,lactose,starch,unknown solution x, and unknown y. One of the questions asks what lab data suggests that not all sugars are reducing sugars. I don't get how we can determine that from the benedict solution because all the solutions changed color. water stayed blue, glucose=orange, fructose=orange, sucrose=green,lactose=orange, starch=murky turquoise, unkonwnx=light green and unknown y=brown. So how do we show not all sugars are reducing sugars from this?