A、Its shape. B、Its size. C、Its location. D、Its brightness. A这位学生所看到的“彩虹”之所以不同寻常是因为它不是半圆形，而是一个完整的圆形。可见，它的不寻常之处在于它的形状，因此选A。

When I was in British Columbia last July working at the department’s archaeological dig, I saw the weirdest rainbow. At first I couldn’t believe my eyes because the bands of color I saw weren’t in a single half circle across the sky. Instead, I saw a full circle of rainbow hues hanging in the sky just above the sea. Inside the circle there was a big white disc and above the circle there was another round band of colors forming a halo. There were curved legs of multicolored light coming off the sides of the circles. It was an incredible sight.
    I ran back to our main camp and tried to get our cook to come with me to see my fantastic find before it disappeared. He just laughed at my exciting story and told me that what I saw was nothing special.., just some "sun dogs". He said I’d be sure to see many more before I left. And sure enough, I did. When I got back from the dig I asked Professor Clark about the "sun dogs," and she’s going to tell us more about them.
26. Why was the student in British Columbia?
27.What did the student find so unusual about the "rainbow" he saw?
28.What was inside the large circle?
29.What did the cook say about the phenomenon the student had seen?
30.What did the cook call the phenomenon?