Final answer:
An increase in acids (H+), CO2, and other metabolic waste products in the tissues would cause a decrease in blood pH.
Step-by-step explanation:
When the body is more active, tissues consume more oxygen and produce more carbon dioxide and acids as waste products. This causes an increase in acids (H+), CO2, and other metabolic waste products in the tissues. As a result, the blood pH drops, leading to an increased acidity in the blood.