They're the only vein that carries oygenated blood
First, he should measure how long it takes for the liquid to become clear if X and Y are mixed together. Then, he should measure how long it takes if he also adds substance A to X and Y. He will find out if substance A is a catalyst.
The answer is 3(x-2)(x+2)
-Water evaporates and condenses into clouds, then the clouds are blown over the ocean, and it rains.
-Water from a mountain flows down and into a river. The river empties into an ocean.
