Blood levels of the readily available fuel, glucose, are tightly regulated by two chemical messengers. One of these, called insulin, decreases blood glucose. The other chemical messenger, called glucagon, increases blood glucose. Both chemical messengers are present at varying levels in the blood at all times. From the choices below, select all of the events that you think will happen in response to a decrease in blood glucose. a. Insulin levels increase b. Insulin levels decrease c. Glucagon levels increase d. Glucagon levels decrease e. Blood glucose levels begin to increase f. Blood glucose levels continue to decrease g. Blood glucose levels remain unchanged