In early civilization, citizens were educated informally, usually within the family unit. Education meant simply learning to live. As civilization became more complex, however, education became more formal, structured, and comprehensive. Initial efforts of the ancient Chinese and Greek societies concentrated solely on the education of males. The post-Babylonian Jews and Plato were exceptions to this pattern. Plato was apparently the first significant advocate of the equality of the sexes. Women, in his ideal state, would have the same rights and duties and the same educational opportunities as men. This aspect of Platonic philosophy, however, had little or no effect on education for many centuries, and the concept of a liberal education for men only, which had been espoused by Aristotle, prevailed.

In ancient Rome, the availability of an education was gradually extended to women, but they were taught separately from men. The early Christians and medieval Europeans continued this trend, and single-sex schools for the privileged through classes prevailed through the Reformation period. Gradually, however, education for women, in a separate but equal basis to that provided for men, was becoming a clear responsibility of society. Martin Luther appealed for civil support of schools for all children. Al the Council of Trent in the 16^th century, the Roman Catholic Church encouraged the establishment of free primary schools for children of all classes. The concept of universal primary education, regardless of sex, had been born, but it was still in the realm of the single-sex school.

In the late 19^th and early 20^th centuries, co-education became a more widely applied principle of educational philosophy. In Britain, Germany, and the Soviet Union the education of boys and girls in the same classes became an accepted practice. Since World War II, Japan and the Scandinavian countries have also adopted relatively universal co-educational systems. The greatest negative reaction to co-education has been felt in the teaching systems of the Latin countries, where the sexes have usually been separated at both primary and secondary levels, according to local conditions. ’

A number of studies have indicated that girls seem to perform better overall and in science in particular. In single-sex classes, during the adolescent years, pressure to conform to stereotypical female gender roles may disadvantage girls in traditionally male subjects, making them reluctant to volunteer for experimental work while taking part in lessons. In Britain, academic league tables point to high standards achieved in girls’ schools. Some educationalists, therefore, suggest segregation of the sexes as a good thing, particularly in certain areas, and a number of schools are experimenting with the idea.

This factory produced ______ motorbikes in 2008 as in the year 2006. A. twice as many B. as twice as many C. as twice many D. as many as twice