资料题：For years the main cause of death in the Third World has been,（　）。

In the English educational system, students take three very important examinations.The first is the eleven-plus, which is taken at the age of eleven or a little past.At one time the ability or aptitude shown on the eleven-plus would have determined if a child stayed in school.Now, however, all children continue in ''comprehensive'' schools, and the eleven-plus deter-mines which courses of study the child will follow.At the age of fifteen or sixteen, the students are tested for the Ordinary Level of the General Certificate of Education.This examination covers a wide range of subjects; once students have passed this exam, they are allowed to specialize, so that two- thirds or more of their courses will be in physics, chemistry, classical languages, or whatever they wish to study at greater length.The final examination, at eighteen, covers only thecontent of the special subjects.Even at the universities, students study only in their concentratedarea, and very few students ever venture outside that subject again; in a real sense, the English boy or girl is a specialist from the age of fifteen.