The Great Wall of China is known to be over 1900 kilometers long, _____16_____ it by far the longest wall
in the world. If it were laid out in a straight line, it _____17_____ 6500 kilometers—as it has many bends and
curves. The building of the wall _____18_____ begun in the third century B.C. by the Emperor Shih Huangti.
The reason it was built was to keep the Huns out of Central Asia. Over the centuries, it _____19_____ added
to, rebuilt and repaired. Not only _____20_____ one of the greatest creations of mankind, but it is also the
only man-made structure visible from space. 【題組】17. (A) reaches (B) will reach (C) reached (D) would reach