There's a general assumption that fluctuations in reproductive hormones cause extreme emotions and that the great majority of women are affected by this.

这里有个普遍的假设，就是生殖激素的波动会导致极端情绪，大多数女性都会受此影响。

And one more thing in this paragraph, the researcher's goal was to understand the effects of sweetened beverages on semen quality and reproductive hormone levels.

在这段话中还有一点，研究者的目标是了解加糖饮料对精液质量和生殖激素水平的影响。

All nine cats--which were named after the wives of American presidents--then had their faeces monitored over the course of two years so that the levels of their reproductive hormones could be checked.

所有九只猫（以美国总统的妻子的名字命名）都在两年的时间里对它们的粪便进行了监测，以便检查它们的生殖激素水平。