Which of the following is true about the immunity to HIV?

About 10 percent of Europe’s present-day population seems to be resistant to HIV -- a significantly higher proportion than on other continents. Researchers have traced this immunity to a genetic mutation that seems to have appeared some 2,500 years ago, and that protects white blood cells against penetration by HIV. From the mid-14th century through the 17th century the prevalence of the mutation increased, in tandem with repeated outbreaks of the plague. The researchers suggest that the mutation protected against the disease, which culled the population of people who lacked it.

US, Australian, and New Zealand scientists report in the journal Lancet that nine factors that people and societies can control cause nearly 2.5 million cancer cases each year. That is about one-third of the seven million annual global total. Leading the list of causes is smoking, which the researchers say is responsible for 20 percent of preventable cancers. Alcohol use and low consumption of fruits and vegetables cause another five percent each. Also significant are overweight and obesity, physical inactivity, urban air pollution, indoor smoke from household cooking, contaminated injections in health clinics, and unsafe sex.