单项选择题

Section 1 　　Directions: Each of the following passages is followed with five questions. For each 　　question there are four choices. Choose the best answer to each 　　question. Then blacken the corresponding letter on the Answer Sheet. 　　Questions 41 to 45 are based on the following passage: 　　If we observe carefully, we can 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 a million. People have made a census (普查) to colors 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 colored 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 (反射) 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 .