单选题：根据以下材料回答第题：Passage fourIt is still sometimes difficult to un

根据以下材料回答第题： Passage four It is still sometimes difficult to understand why those between ages 10 and 18 would endanger their lives by joining armed forces or rebel groups and become fighting soldiers. The recently published book, Young Soldiers, Why They Choose to Fight by Rachel Brett and Irma Specht, tries to find an answer.
There is no doubt that children fight in most armed conflicts today. While international attention focuses largely on those who are forced into battles, thousands more enlist(应征入伍) voluntarily.
In an attempt to understand the young who take up arms, Brett and Specht interviewed 53 boy and girl soldiers and ex-soldiers from around the world, Afghanistan, Colombia, the Republic of the Congo for example. All interviewees were involved with armed groups before the age of 18 and all classified themselves as volunteers.
What these two field officers heard is “I joined involuntarily—if you have nothing, you volunteer for the army”. Other reasons young people gave are self—defense, revenge, poverty, and unemploy-ment.
But while it is common knowledge that most child soldiers come from poor and disadvantaged backgrounds, Young Soldiers shows that the issue is far more complex. Many poor child do not join the army. The environmental, educational, social, cultural, and highly personal factors determine whether someone decides to join up or not.
The battlefield is not a place children. One young soldier described being there as “too sad an experience”. The authors hope that by understanding why teenagers join up, those child soldiers should know how to discourage others from the same tragedy.Young Soldiers, Why They Choose to Fight is () A．a book
B．a magazine
C．a news report
D．a TV program