I have just come home after viewing some a

问题：

I have just come home after viewing some astonishing works of art that were recently discovered in Church Hole cave in Nottinghamshire. They are not drawings, as one would expect, but etchings, and they depict a huge range of wild animals. The artists who created them lived around 13,000 years ago, and the images are remarkable on a variety of counts. First of all, their sheer number is staggering. There are ninety all together. Moreover, fifty-eight of them are on the ceiling. This is extremely rare in cave art, according to a leading expert, Dr. Wilbur Samson of Central Midlands University. "Wall pictures are the norm," he says. "But more importantly, the Church Hole etchings are an incredible artistic achievement. They can hold their own in comparison with the best found in continental Europe." I am not a student of the subject, so I have to take his word for it. However, you do not have to be an expert to appreciate their beauty.

In fact, it is the wider significance of the etchings that is likely to attract most attention in academic circles, since they radically alter our view of life in Britain during this epoch. It had previously been thought that ice-age hunters in this country were isolated from people in more central areas of Europe, but the Church Hole images prove that ancient Britons were part of a culture that had spread right across the continent. And they were at least as sophisticated culturally as their counterparts on the mainland.

An initial survey of the site last year failed to reveal the presence of the etchings. The reason lies in the expectations of the researchers. They had been looking for the usual type of cave drawing or painting, which shows up best under direct light. Consequently, they used powerful torches, shining them straight onto the rock face. However, the Church Hole images are modifications of the rock itself, and show up best when seen from a certain angle in the natural light of early morning. Having been fortunate to see them at this hour, I can only say that I was deeply and unexpectedly moved. While most cave art often seems to have been created in a shadowy past very remote from us, these somehow, convey the impression that they were made yesterday.

Dr. Samson feels that the lighting factor provides important information about the likely function of these works of art. "I think the artists knew very well that the etchings would hardly be visible except early in the morning. We can therefore deduce that the chamber was used for rituals involving animal worship, and that they were conducted just after dawn as a preliminary to the day’s hunting."

To which I can only add that I felt deeply privileged to have been able to view Church Hole. It is a site of tremendous importance culturally and is part of the heritage, not only of this country, but the world as a whole.

Why were the images not discovered during the initial survey？（）

A．Traditional way of viewing was employed.

B．People were not expecting to find any images.

C．Modern equipment was used to explore the cave.

D．The torches the researchers used were not powerful enough.