关于经前期综合征的原因有很多学说，但是都没有明确的生理学的触发器被鉴定过。

There are many theories about the causes of PMS, but no definite physiological trigger has been identified.

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我把这件作品给某位旧约教授鉴定过，他认为那些文字要不就是不具有任何意义和价值。

I showed this to an ot professor and his conclusion was that most likely this does not mean much or worth much.

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全部鉴定试验结果显示新的刹车装置与已鉴定过的现役C/C刹车盘相比具有良好的刹车性能，达到了全部要求。

The test results indicate that the C/C brake disks have satisfactory properties in terms of friction and wear, density, thermal and mechanical properties etc.

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