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| 保护环 | |||
| 磁带卷保护环 | |||
| protection ring: 13 phrases in 8 subjects |
| Computer networks | 1 |
| Electric machinery | 1 |
| Hydroelectric power stations | 1 |
| Information technology | 3 |
| Management | 1 |
| Mathematics | 1 |
| Space | 1 |
| Technology | 4 |
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