Final answer:
The modifiable risk factor is smoking cigarettes.
Step-by-step explanation:
A modifiable risk factor for disease is one that can be changed or controlled. In the given options, the modifiable risk factor is b. The patient smokes two packs of cigarettes every day. Smoking cigarettes is a known risk factor for many diseases, including lung cancer, heart disease, and respiratory problems. By quitting smoking, the patient can reduce their risk of developing these diseases.