The Bush administration is giving public school districts broad new latitude to expand the

number of single-sex classes, and even schools, in what is widely considered the most significant policy change on the issue since a landmark federal law barring sex discrimination in education more than 30 years ago.

Two years in making, the new rules, announced Tuesday by the Education Department, will allow districts to create single-sex schools and classes as long as enrollment is voluntary. School districts that go that route must also make coeducational schools and classes of "substantially equal" quality available for members of the excluded sex.

The federal action is likely to accelerate efforts by public school systems to experiment with single-sex education, particularly among charter schools. Across the nation, the number of public schools exclusively for boys or girls has risen from 3 in 1995 to 241 today, said Leonard Sax, executive director of the National Association for Single Sex Public Education. That is a tiny fraction of the approximately 93,000 public schools across the country.

"You're going to see a proliferation of these," said Paul Vallas, chief of schools in Philadelphia, where there are four single-sex schools and plans to open two more. "There's a lot of support for this type of school model in Philadelphia."

Until now, Mr. Vallas said, there had been a threat of legal challenge that had delayed, for example, a boys' charter school from opening in Philadelphia this September. New York City has nine single-sex public schools, most of which opened in the past four years.

While the move was sought by some conservatives and urban educators, and had backing from both sides of the political aisle, a number of civil rights and women's rights groups condemned the change.

"It really is a serious green light from the Department of Education to re-instituting official discrimination in schools around the country," said Marcia Greenberger, a co-president of the National Women's Law Center.

Under Title IX, the 1972 law that banned sex discrimination in educational institutions that receive federal funds, single-sex classes and extracurricular activities are largely limited to physical education classes that include contact sports and to sex education.

To open schools exclusively for boys or girls, a district has until now had to show a "compelling reason", for example, that it was acting to remedy past discrimination.

But a new attitude began to take 'hold with the passage of the No Child Left Behind Law in 2002 when women senators from both parties came out in support of same-sex education and asked the Education Department to draft guidelines to permit their growth.

The new rules, first proposed by the Education Department in 2004, are designed to bring Title IX into conformity with a section of the No Child Left Behind Law that called on the department to promote single-sex schools.

What is the requirement for the districts to create single-sex schools？

A．There should be coeducational schools.

B．There should be quality classes available to both sexes.

C．There should be voluntary enrollers in such schools.

D．There should be equal approach to both single-sex classes and coeducational classes.