Most of the flowers in nature are red, orange and yellow. If we have seen a black flower, it's a chance in million. People have made a census (  ) to colors of more than four thousand kinds of flowers and discovered that only eight of them are black. As we know, sunlight is formed by seven different colored lights. The wave length of each light is different, so the quantity of heat in each light is also different. Flowers, especially their petals (  ) , are easy to be harmed by high temperature. Black flowers can take in all the light waves which cause the flowers to dry up in a high temperature. So black flowers can rarely survive sunlight. But red flowers, orange flowers and yellow flowers can protect themselves from sunlight by reflecting the red light, orange light and yellow light, each of which has a large quantity of heat. The passage tells us that   _  .
black flowers are so weak that it is difficult for them to grow up. there is only eight black flowers in nature. sunlight is formed by seven different colored lights, so the wave length of each light is different. black flowers can take in the light of all the wave lengths which make them dry up because of high temperature.