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问题 填空题

为保证光纤通信系统的色散性能更好，要求发送机发送的光信号的谱线宽度（）。

答案

参考答案：越窄越好

填空题

婴幼儿上颌骨骨髓炎行搔刮术时搔刮应__________，只将__________或摘除、以免破坏__________，损伤__________，造成术后畸形。
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选择题
The construction of the two new railway lines _____ by now.

A. has completed
B. have completed
C. have been completed
D. has been completed
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