In this complex, fluid environment, providing an appropriate measure of oversight and control can be a major challenge.

在这个复杂的变换的环境当中，提供一个合适的方法来控制和监督将是一个主要挑战。

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Allantoic fluid of chicken embryo that had been inoculated with one strain of renal type IBV was used to challenge 16-day-old chicken.

用鸡肾型传支病毒（IBV）分离株的鸡胚尿囊液接种16日龄蛋雏鸡，并随机分为对照组、中药治疗组和卵抗治疗组。

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Objective to study the association of composition in plaque fluid after sugar challenge wi th caries susceptibility in order to find predictors of identifying individual caries risk.

目的研究糖代谢后牙菌斑液化学成分与龋的关系，探求判别个体龋易感性中的因子。

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"The 67-year-old Mirren rises to the daunting technical challenge with a quite uncannily fluid lightness of touch as she shifts back and forth on an age-spectrum of six decades, " wrote The Independent's Paul Taylor.

BBC: Helen Mirren is 'magnificent' as the Queen in The Audience

At that depth stopping the flow with a deadweight of drilling fluid should create few problems, once the exceedingly difficult challenge of hitting the well is met.

ECONOMIST: The Gulf oil spill