Britain had reached the fourth stage of the demographic transition.

英国已经达到了人口转变的第四阶段。

But actually most of the world's countries have made it to the fourth stage.

实际上，世界上大多数的国家都已经到了第四阶段。

The fourth stage is retrieval, and it occurs in the prefrontal cortex, hippocampus, and cortex.

第四阶段是检索，发生在前额叶皮质、海马体和大脑皮层处。

This puts you back to the second stage, education which then leads to the third stage-application, which leads again to the fourth stage, refinement and on and on and on.

这会让你回到第二阶段，教育阶段，然后是第三阶段，应用阶段，再次是第四阶段，精益求精。

Sometimes the several-hours after delivery is called the " fourth stage" , because there are major physiologic changes like adaption to the blood loss, and the start of uterine involution, where the uterus begins returning to its pre-pregnant state.

有时分娩后几个小时称为“第四产程”，因为有很多重要的生理变化，例如血液流失的适应，以及子宫复旧的开始，子宫回到产前的状态。

Due to the mechanics of our sleep cycles during the fourth stage of sleep called rapid eye movement or rim, we experience a loss of muscle tone that naturally stops our arms and legs from controlled movement.

由于我们的睡眠周期机制在睡眠的第四阶段称为快速眼动或边缘，我们会经历肌张力的丧失，自然会阻止我们的手臂和腿受控运动。