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| frequency-tracking | |||
| 频率 跟 踪: 16 phrases in 8 subjects |
| Air defense | 2 |
| Astronautics | 1 |
| Communications | 1 |
| Electronics | 5 |
| Geophysics | 1 |
| Shipbuilding | 1 |
| Space | 4 |
| Telecommunications | 1 |
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