下表列出了相同条件下不同物质密度及声音在其中传播的速度，根据表中提供的信息，可以得出的结论是（    ）

    What do you eat every day? Some people think about it. And some people will not make plans for their meals.

    Many people like to have fast food near their offices. This kind of food can make them fat and it is bad for their health. Even it will make them ill when they are old.

   What should a healthy person eat every day? Well, I will tell you the 'healthy eating habit(习惯)'. It comes from doctors.

     When people do a lot of work, the energy is burning(燃烧). So you need noodles, rice, milk, bread and eggs. If you don't eat them, you will feel tired. You should eat fruits and vegetables, too. There are a lot of vitamins（维生素） in them. They can make you strong. And they can give you water.

某学校的生物课外小组开展大白菜丰产实验，每棵重约4Kg。请问大白菜增产的物质主要来自                                                    （   ）

阅读漫画，回答问题。