Rainbows are spectacular (壯觀的) rays (光束) of color. Sunlight looks white, but it really has different colors: red, orange, yellow, green, blue, indigo, and violet. The sun makes rainbows when white sunlight passes through raindrops (雨滴).         We need three conditions (條件) to see a rainbow. First, it has to be raining. Second the sun has to be shining. Third, we have to be between the sun and the rain.          A rainbow is an optical illusion, so you just can’t catch up to it. When you move, it moves too!

【題組】40.In general (一般而言), how many colors do rainbows have?
(A)3
(B) 7
(C)17
(D) 70