Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 31 to 35.

 A rainbow is an optical display of color that usually appears in the sky when a beam of sunlight refracts through millions of raindrops. Each (31)________ color from the spectrum is then sent to your eyes. For this to happen, the angle between the ray of light, the raindrop and the human eye must be between 40 and 42 degrees.

 After studying rainbows in (32)________, Sir Isaac Newton was able to explain how they are formed. However, he was color blind, so he had to rely on the eyes of his assistant, who could easily (33)________all the seven colors: red, orange, yellow, green, blue, indigo and violet. His assistant could also clearly tell the difference between indigo and violet.

 There are two types of rainbows. Primary rainbows are the most common and have the most distinctive colors, with red appearing on the outside of the arc and violet on the inside. Secondary rainbows are unusual because the light is reflected twice within the raindrop before it (34)________ a rainbow, so the colors are in reverse order and not as bright as primary rainbows.

 There is a popular myth that if you reach the end of a rainbow, you will find a pot of gold waiting for you. In fact, it is impossible to do this, because a rainbow has no end - as you go towards the point where the rainbow seems to touch the ground, it moves away from you as quickly as you (35)________.

Điền vào ô 31