| 摘要 |
An apparatus includes an upper portion, a sole and a fin. The upper portion is configured to at least partially cover a foot. The sole is coupled to the upper portion and defines a cavity. The fin has a first portion and a second portion. The fin is movable between a first configuration and a second configuration. When in the first configuration, the fin is substantially within the cavity defined by the sole, and the first portion of the fin at least partially overlaps the second portion of the fin. When in the second configuration, the fin extends substantially outside the cavity defined by the sole.
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