The statement that best reflects how changes in public policy have affected smoking is: "The dangers of smoking are well known by most people."
This can be attributed to various public health campaigns and regulations, such as warning labels on cigarette packages, restrictions on advertising, and educational programs. These efforts have raised public awareness about the health risks associated with smoking, leading to a decline in smoking rates over the years. The other statements either exaggerate the impact of policy changes (like claiming there is no risk from second-hand smoke) or refer to specific regulations that may not have been universally enacted (like the sale of tobacco in grocery stores).