VOA慢速英语:Broccoli and Cauliflower - Their Tops Make Good Eating

are high in富含……

相当于：

be rich in富于,盛产,有很多…

例句：Those countries are rich in mineral resources.
      那些国家矿物资源很丰富。

abound in充满,有大量的…,盛产…

例句：The English language abounds in phrasal verbs.
     英语里有大量的短语动词。

2.Harvest the center flower-bud cluster of broccoli when it reaches the size you want and while the buds are still tightly together.

这句话的前半部分是主句，Harvest the center flower-bud cluster of broccoli，后面的when and while都是状语。

3.The less time they cook, the better.

the +比较级……, the+比较级”，表示“越……越……”。

　　The more money you make, the more you spend.
　　钱你赚得越多，花得越多。

　　The sooner，the better.
         越快越好。