What is the most difficult educational toy?
To find this rare educational toy, you can go to the website of "Beijing University Student Educational Toys Club", where there are more than 300 kinds of educational toys, all different. In fact, it is not difficult to connect nine chains, but it is cumbersome. I think Huarong Road is more difficult. Their website is called "Solve the riddle", and Baidu can see it at once.