In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.

Article: Fumbling with the buttons to find a good song while driving has been linked to increased risk of crashes, but is listening to music risky? "It depends on the music," says a report published in the October issue of Accident Analysis & Prevention. The study found teenage drivers who played their own music had significantly more traffic violations compared with background music designed by the researchers to minimize driving distractions, or no music. Researchers at Ben-Gurion University in Israel recruited 85 drivers about 18 years old; just over half were male. The _ were each assigned to drive six challenging road trips that were about 40 minutes long, accompanied by an experienced driving instructor. Music was played on four trips, two with selections from the drivers' playlists, mostly fast-paced vocals, and two with background music, which was a mixture of easy listening, soft rock and light jazz designed to increase driver safety. No music was played on two trips. Subjects rated their mood after each trip and in-car data recorders analyzed driver behavior and errors. All 85 subjects committed at least three errors in one or more of the six trips; 27 received a warning and 17 required steering or braking by an instructor to prevent an accident. When the music was their own, 98% made errors; without the music, 92% made errors; and while listening to the safe-driving music, 77% made errors. Speeding, following too close, inappropriate lane use, one-handed driving and were the common violations. The male subjects were more aggressive drivers and made more serious errors than female subjects. The teens played their own music at a very loud volume but significantly decreased the sound level when listening to the safe-driving music, researchers said. Mood ratings were highest on trips with driver-preferred music.
Answer: increase drivers' safety
In the research, soft rock and light jazz are likely to _ .