Which of the following is the best way to ensure you are receiving the best possible nutrition?
a. eating whole grains every morning and evening
b. reducing the amount of salt and sugar in foods
c. eating a wide variety of foods
d. using olive oil instead of butter for cooking

I would choose letter c. eating a wide variety of foods.  This best summarizes the other three choices.  The others were also good recommendations but letter embodies the practice of a balance diet wherein you eat from each of the important food groups to maintain good health.

Smoking damages the respiratory system by inhalation of a foreign substance, that is absorbed and residue is left behind on our lungs sponge like substance. the gas that is inhaled also increase your blood pressure and dilates your blood vessels. also the process of inhaling and exhaling the smoke it causes irritation to the throat and mouth. smoking can cause lung cancer and other respiratory and circulatory diseases.