The "It's a Pop Quiz!" Bonus Question was "Every year in the U.S., how many millions of teenagers get a sexually transmitted infection?" Answer choices were: (a) 3 million, (b) 1 million, (c) 2 million, or (d) 5 million.

The answer: (a) three million.

You can learn more about sexually transmitted infections (STIs) by reading these SEX, ETC. stories. Or check out the info from our answer source, the Alan Guttmacher Institute.

Got a question about STIs? Call the CDC National STD & AIDS Hotlines at (800) 342-2437 or (800) 227-8922. (The hotlines are open 24/7.) Or go to Ask the Experts.