is defined as a chronic lung disease caused by cigarette smoking and is characterized by difficulty in breathing and shortness of breath.

Many organs are involved in the processes of keeping the blood and the body clean. when poisonous or harmful substances are in the blood, they are absorbed by the and released in a less harmful form. when wastes are present in the blood, they are filtered out and removed from the body by the

What is the most appropriate method of gaining weight (muscle mass)

In the water cycle , when does water undergo a chemical change