题目

  11   People traveled in search of food and shelter or in order to flee from their enemies. Sometimes they were looking for gold or silver in order to become rich. On other occasions they were searching for rich farmland.      This is not to say that no one ever traveled just for fun. Even in ancient times, some pleasure travel occurred. During a typical season, 700,000 tourists would crowd into the ancient city of Rome, where animals performed and magicians entertained them.    12            13   International tourist arrivals alone reached as many as 546 mill14．小球A自h高处静止释放的同时，小球B从其正下方的地面处竖直向上抛出，欲使两球在B球下落的阶段于空中相遇，则小球B的初速度应满足何种条件？