| 摘要 |
PURPOSE: A hoop having a groove is provided to improve concentration and to enable a user to roll one or more rings. CONSTITUTION: A hoop having a groove is as follows. A groove is formed inside the hoop. A stick(1) is inserted into the groove in order to roll the hoop. A second hoop is rolled. The second hoop is placed in the front of the first hoop. In the second hoop, a groove is formed. Third and fourth hoops are formed.
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