A、The homeless are willing to live under a bridge or in a cardboard box. B、You will not find homeless people in countries with a

In many countries the standard of living enjoyed by their people has increased rapidly in recent years. Sadly, not everyone in these countries is so fortunate and many people in rich countries are homeless.
    The reasons for homelessness are various, but poverty is undoubtedly one of the main causes. The homeless people may have become jobless and then been unable to pay their rent and so no longer have a roof over their heads. Often, the fact that unemployed people get help from the government prevents this from happening, but not always.
    Some homeless people are mentally ill and have no one to look after them. Some are young people who, for one reason or another, have left home and have nowhere to live. Many of them have had a serious disagreement with their parents and have left home, choosing to go to a city and live on the streets. Sometimes they have taken such action because they have been unable to get on with a stepparent.
    Many homeless people get into the habit of begging to get enough money to stay alive, but many of the general public refuse to give anything to beggars. Often they are moved on by the police, being accused, whether rightly or wrongly, of forceful begging. There are many who disrespect homeless people.
    Some cynics declare that homeless people choose to live the life which they lead. But who would willingly choose to live in a shop doorway, under a bridge or in a cardboard box?
Questions 29 to 31 are based on the passage you have just heard.
29. According to the passage, what causes some young people to be homeless?
30. What can we infer from the passage?
31. In the passage, what does "a roof over their heads" most probably refer to?