Under what circumstances should the last name of only the first author of a three- to five-author reference, followed by et al. be included with the citation in the body of the text?

In 1993, the Environmental Protection Agency declared that

A. sidestream smoke is lower in nitrosamines. B. secondhand smoke is a known carcinogen that increases lung cancer risk. C. smoking would be banned in all federal facilities. D. cigarette smoking might be a cause of heart disease.

After speaking to your 21-year-old brother, you discovered that he has driven while he was intoxicated several times during the past few months. What percentage of college students report having driven intoxicated within the past year?

70% || 50% || 30% || 10% || || ||