| 摘要 |
The fence system includes a trench and a collapsible screen which is mounted in the trench. A lifting device engages the top of the screen and the latter in fixed inside the trench. The lifting device is designed to raise the top of the screen to an extended position at a predetermined height, and also to lower it to a retracted position inside the trench. A closure is provided which closes the trench when the screen is collapsed in retracted position.
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