A pedestrian was struck and killed by a car on William Day Boulevard at L Street in South Boston Wednesday evening, according to Jake Wark, a spokesman for the Suffolk district attorney’s office. The victim, who was not identified, was an adult male, Wark said. Members of the State Police Collision Analysis and Reconstruction section, Crime Scene Service Section, investigated the accident along with state troopers assigned to the district attorney’s office. Boston EMS also responded to the scene.