Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions.

Educating children at home as an alternative to formal education is an option chosen by families in many parts of the world. The homeschooling movement is popular in the United States, where close to one million Children are educated at home. In Canada, 1 percent of school-age children are homeschooled, and the idea also enjoys growing popularity in Australia, where 20,000 families homeschool their children. The movement is not limited to these countries. Homeschooling families can be found all over the world, from Japan to Taiwan to Argentina to South Africa.

Homeschooling is not a novel idea. In fact, the idea of sending children to spend most of their day away from home at a formal school is a relatively new custom. In the United States, for example, it was not until the latter part of the nineteenth century that state governments began making school attendance compulsory. Before that, the concept of a formal education was not so widespread. Children learned the skills they would need for adult life at home from tutors or their parents, through formal instruction or by working side by side with the adults of the family.

In the modern developed world, where the vast majority of children attend school, families choose homeschooling for a variety of reasons. For people who live in remote areas, such as the Australian outback or the Alaskan Wilderness, homeschooling may be their only option. Children who have exceptional talents in the arts or other areas may be homeschooled so that they have more time to devote to their special interests. Much of the homeschooling movement is made up of families who, for various reasons, are dissatisfied with the schools available to them. They may have a differing educational philosophy, they may be concerned about the safety of the school environment, or they may feel that the local schools cannot adequately address their children's educational needs. Although most families continue to choose a traditional classroom education for their children, homeschooling as an alternative educational option is becoming more popular.

What does the word "that" in paragraph 2 refer to?