Answer: i
Why?
Let's look at the title and underline the key words: The health effects of smoking
Now let’s find synonyms or paraphrases for the key words:
Health effects: diseases, illnesses, health problems, issues, symptoms, consequences, cause
Smoking: smoke, cigarette, tobacco, cigars
Now let’s have a look at words in the paragraph that match or relate to those synonyms/paraphrases:
Smoking leads to disease and disability and harms nearly every organ of the body. More than 16 million Americans are living with a disease caused by smoking. For every person who dies because of smoking, at least 30 people live with a serious smoking-related illness. Smoking causes cancer, heart disease, stroke, lung diseases, diabetes, and chronic obstructive pulmonary disease (COPD), which includes emphysema and chronic bronchitis. Smoking also increases risk for tuberculosis, certain eye diseases, and problems of the immune system, including rheumatoid arthritis. Cigarette smoking causes more than 480,000 deaths each year in the United States. This is nearly one in five deaths. More than 10 times as many U.S. citizens have died prematurely from cigarette smoking than have died in all the wars fought by the United States. Smoking causes about 90% (or 9 out of 10) of all lung cancer deaths. More women die from lung cancer each year than from breast cancer.
Now that we found those key words, we can skim (read quickly) around them:
Smoking leads to disease and disability and harms nearly every organ of the body. More than 16 million Americans are living with a disease caused by smoking. For every person who dies because of smoking, at least 30 people live with a serious smoking-related illness. Smoking causes cancer, heart disease, stroke, lung diseases, diabetes, and chronic obstructive pulmonary disease (COPD), which includes emphysema and chronic bronchitis. Smoking also increases risk for tuberculosis, certain eye diseases, and problems of the immune system, including rheumatoid arthritis. Cigarette smoking causes more than 480,000 deaths each year in the United States. This is nearly one in five deaths. More than 10 times as many U.S. citizens have died prematurely from cigarette smoking than have died in all the wars fought by the United States. Smoking causes about 90% (or 9 out of 10) of all lung cancer deaths. More women die from lung cancer each year than from breast cancer.
Wherever those key words are located, some disease or health issue is mentioned. It is therefore very clear that the focus throughout this paragraph is the effects of smoking. Not only is it the starting argument, but those key words are spread consistently all over the text, therefore suggesting this is the focus of the paragraph.