in ancient Egypt people noticed the season when the Nile flooded the land was followed by the season when crops were plant and cared for.
(翻译并分析，被两个when搞蒙掉。)

I was in the kitchen cooking something(跟I was cooking in the kitchen 有什么不一样？)

Don't we have any food for supper（跟Do we haven't any food for supper有什么不同？）

Native Americans express their anger over this business deal （over 在这里什么意思）

1.in ancient Egypt people noticed the season when the Nile flooded the land was followed by the season when crops were plant and cared for. 
在古埃及，人们知道在尼罗河泛滥过后，就是播种和照料庄稼的季节
第一个when ,when the Nile flooded the land，尼罗河泛滥后的时候
第二个when,when crops were plant and cared for ，种庄稼的时候
两个when：第二个when就是在第一个when发生后

2.I was in the kitchen cooking something(跟I was cooking in the kitchen 有什么不一样？) 
强调的不一样，前面强调在厨房里，后面的用法强调在煮东西

3.Don't we have any food for supper（跟Do we haven't any food for supper有什么不同？） 
差不多，但是都是用前面的表示方法，没见过用后面的。

4.Native Americans express their anger over this business deal （over 在这里什么意思）
表示在这单生意上，over是介词，和in类似，更多表示从头到尾。