Hong Kong security forces arrested 180 people, including several under the age of 18, in the aftermath of the most violent clashes yet in four months of anti-government unrest. More than 100 people were injured Tuesday, China’s National Day celebrating 70 years as a republic, including an 18-year-old student who was shot in the chest during a scuffle with police. Hundreds of office workers and high-school students held a sit-in at the injured student’s school Wednesday to protest the shooting of the student, who is in stable condition. Authorities are looking for ways to stop the violent protests, but say they have had made little headway in negotiating with the pro-democracy forces.