4/20: Signifies cannabis culture.

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1978: Soviet fighters shot Korean Air Lines Flight 902 after it violated Soviet airspace, forcing it to make an emergency landing due to damage.

1989: Last Canadian $1 bills roll off the presses. The passing of the buck came two years after the introduction of the Loonie, bringing an end to 119 years of the paper dollar.

1999: Two seniors killed 12 of their classmates and a teacher before committing suicide at Columbine High School.

2008: American Danica Patrick won the Indy Japan 300, becoming the first woman to win an IndyCar auto race.