Troops shot and killed a 20-year-old Palestinian and wounded two others during clashes that erupted after Israeli authorities tried to collect taxes in a Gaza City neighborhood. Arab hospital officials said Ahmed Muharam died after being shot in the heart. The withholding of taxes has been a frequently used tactic by Arabs during their 14-month-old uprising. Meanwhile, in the West Bank city of Nablus, troops demolished the top floor of the building from which Palestinians dropped a concrete block that struck and killed an Israeli soldier last Friday, an army spokesman said. Soldiers also sealed windows facing the alley, the army said.