All over the world people began their exciting day by drinking a cup or several cups of coffee. People have always said that a cup of coffee in the morning helps them begin their day on the right foot. They need this cup of coffee to get going in the morning. It is not the coffee but something in the coffee that activates our bodies and brains. It is a material called caffeine. Caffeine may increase a person's mental   and physical abilities. For example, two cups of coffee will _ blood flow, breathing, and body heat production by 10% to 20%. All of this make your heart beat faster and doctors warn   that this may be somewhat dangerous. Caffeine is found in tea, coffee, chocolate, and many other common foods. A little caffeine is probably helpful. But too much caffeine can result in nervousness and sleeplessness. A cup of coffee will make your blood move faster by  _  .
5% to 10% 10% to 20% about 15% about 20%