单项选择题

More than 6,000 children were expulsed (开除) from U.S. schools last year for bringing guns and bombs to school, the U.S. Department of Education said on May 8.
The department gave a report to the expulsions as saying handguns accounted for 58 percent of the 6,093 expulsions in 2003-2004, against 7 percent for rifles(步枪) or shotguns and 35 percent for other types of firearms. "The report is a clear sign that our nation’s public schools are cracking down(严惩) on students who bring guns to school," Education Secretary Richard Riley said in a statement. "We need to be strong-minded about keeping guns out of our schools and do everything to keep our children safe. " In March 2004, an 11 years old boy and 13 years old boy using hand-guns and rifles shot dead four children and a teacher at a school in Jonesboro, Arkansas. In October, two were killed and seven were wounded in a shooting at a Mississippi school. Two months later, a 14 years old boy killed three high school students and wounded five in Dasucah, Kentucky. Most of the expulsions, 56 percent, were from high schools, which have .students from about age 13. 34 percent were from junior high schools and 9 percent were from elementary schools, the report said.
From the first paragraph we can infer that in the U.S. schools______.