一般而言，杀虫蛋白的含量在棉花生长发育的前期较高，到中期时有所下降，但到晚期时则又有回升。

Generally, insecticidal protein levels were high during the early stages of cotton growth; they declined in mid-season, and rebounded in late season.

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出现这种空缺的原因并不明确，但最有可能要归结到晚期投资者身上。

There is no definitive reason for the vacancy, but the most likely culprits are late-stage investors.

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