Final answer:
Seven members of Bugsy Moran's gang were victims of the St. Valentine's Day Massacre on February 14, 1929, which occurred during the Prohibition era as a result of gang rivalry in Chicago.
Step-by-step explanation:
The event on February 14, 1929 that saw 7 members of Bugsy Moran's gang falling victim to violence was A) The St. Valentine's Day Massacre. The gruesome event took place in Chicago and was a result of the intense rivalry between the city's most powerful crime syndicates: the South Side Italian gang led by Al Capone and the North Side Irish gang led by Bugs Moran. On that day, several members of Moran's gang were lured into a garage and gunned down by men posing as police officers, which turned out to be one of the most infamous gangland killings in American history.