将浸泡后的玉米种子从中央纵向剖开，并在剖面上滴一滴碘液，被染成蓝色的部位是（　　）

阅读理解

    Every country has its favourite food. In some countries, people(人们) eat rice every day. They often eat it with meat, fish and vegetables.       

   Japanese(日本人) eat a lot of fish, and they eat a lot of rice, too. In England(英国), the favourite food is fried fish and French fries. In the USA(美国) people like hamburgers a lot. And they like to have cold drinks. In Canada, people eat bread with butter(黄油) on it. In India, people like to eat hot food. Some people eat only fruit and vegetables. They don't like to eat meat and fish. They think green food is good for them.

已知扇形的周长为20，当扇形的圆心角为____ 弧度时，它有最大的面积．

叶圣陶先生指出：“心里知道该怎样，未必就能养成好习惯；必须怎样怎样去做，才可以养成好习惯。”这句话表明，要养成好习惯应该（  ） 

下列有关玉米种子的说法，正确的是（ ）