The history of the yo-yo is somewhat up in the air. No one really knows who first put two disks together with a small axle(轮轴)separating the halves and then tied a string to the axle and wound it up. Some historians say it was developed in ancient Greece, India, or China. We do know, however, that the toy first became popular in both England and France in the late 18th century. The first modern yo-yos were introduced in the United States by Donald F. Duncan in the late 1920s. He is credited with popularizing (though probably not inventing)the slip-string yo-yo, which enables a yo-yo to "sleep". The yo-yo first became popular in the 1930s, when Duncan sent out teams of travelling yo-yo men (not women, mind you)who would spend three, four, and five weeks in cities and towns across America, teaching tricks, selling yo-yos, and running contests. The yo-yo reached fad (时尚)levels in the late 1940s, throughout the 1950s, and into the early 1960s. By then almost every kid in America had a yo-yo. But the Golden Days of yo-yo unfortunately ended when Duncan, who had manufactured more yo-yos than it could sell, went bankrupt in 1965, shortly after the yo-yo boom had suddenly ended. The travelling professional yo-yoers soon disappeared, and the toy began to lose some of its appeal. However, the yo-yo was not to be defeated. It experienced a major revival in the early 1970s, and today, the yo-yo is experiencing its greatest popularity yet. It is learnt from the first paragraph that _______.A. early yo-yo was different from what it is like nowB. some historians are sure of the origin of yo-yoC. it is not understandable why yo-yo is so popularD. no one is certain who invented yo-yo

The history of the yo-yo is somewhat up in the air. No one really knows who first put two disks together with a small axle(轮轴)separating the halves and then tied a string to the axle and wound it up. Some historians say it was developed in ancient Greece, India, or China. We do know, however, that the toy first became popular in both England and France in the late 18th century.

The first modern yo-yos were introduced in the United States by Donald

• F. Duncan in the late 1920s. He is credited with popularizing (though probably not inventing)the slip-string yo-yo, which enables a yo-yo to "sleep". The yo-yo first became popular in the 1930s, when Duncan sent out teams of travelling yo-yo men (not women, mind you)who would spend three, four, and five weeks in cities and towns across America, teaching tricks, selling yo-yos, and running contests.
  
  The yo-yo reached fad (时尚)levels in the late 1940s, throughout the 1950s, and into the early 1960s. By then almost every kid in America had a yo-yo. But the Golden Days of yo-yo unfortunately ended when Duncan, who had manufactured more yo-yos than it could sell, went bankrupt in 1965, shortly after the yo-yo boom had suddenly ended. The travelling professional yo-yoers soon disappeared, and the toy began to lose some of its appeal. However, the yo-yo was not to be defeated. It experienced a major revival in the early 1970s, and today, the yo-yo is experiencing its greatest popularity yet.
  
  It is learnt from the first paragraph that _______.
• A. early yo-yo was different from what it is like now
• B. some historians are sure of the origin of yo-yo
• C. it is not understandable why yo-yo is so popular
• D. no one is certain who invented yo-yo