If we observe carefully, we van find that 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(普查)to colours of more than four thousand kinds of flowers and discovered that only eight of them are black. Why?
As we know, sunlight is formed by seven different kinds of coloured light. The wave length of each light changes, so the quantity of heat in each light changes, too. Flowers, especially their petals(花瓣), are very delicate(纤弱) and prone(易于) to the harm caused 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.
That is why red, orange and yellow flowers are very common in nature while black flowers are so rare.
We can hardly find black flowers because  _____.

A．they are so weak that it’s difficult for them to grow up

B．there are no black flowers in the world.

C．the petals of black flowers are very delicate

D．they can take in the light of all wave lengths, which make the flowers dry up

Sunlight is formed by _____.

A．many different kinds of coloured light

B．three different kinds of coloured light—red, orange and yellow

C．seven different kinds of coloured light

D．four thousand kinds of coloured light

The red, orange or yellow light contains _____.

A．less heat than the other lights	B．more heat than the other lights
C．a great deal of heat	D．a little heat

“It is a chance in a million” means_____________

A．it is common

B．it is extremely rare

C．it’s lucky

D．it’s impossible