History is the story of us, human beings. Everyone who has lived and everything that has h____ are part of history. But history is not only what happened in the past. The word also means the study of the past, through old w____records and other kinds of facts.

    Why do we study history? One r____is that we enjoy it. A good story is even better if it is true, and history is full of good s____though they can be terrible too. A more serious reason is to understand o____and the world we live in. To understand events happening now, we need to know their causes. We cannot understand the p____if we know nothing about the past. History helps us understand why things are the way they are.

    Of course, history books cannot tell us everything about the past, not even everything that i____recorded. A history of the world has to pick out the people and events t____changed the world.

    Since ancient times, great civilizations have appeared in d____countries and regions. Usually, only three or four existed at the same time. While they lasted they changed the l____not only of their own people, but of their neighbors, today.

青春期是____逐渐发育为____的过渡时期。女孩的青春期一般为____岁，男孩的青春期一般比女孩____2年左右。青春期，随着____器官的发育成熟，人的身体会发生一些重要的生理和外表变化，个子迅速____。男孩骨骼强健，____发达；女孩____和____明显增大，身体呈现出柔和的曲线。