题目

Our nearest neighbor is the moon．In the sky，the moon and the sun seem to be of the same size because the moon is much nearer． The moon makes the tides--the changes in the level of the sea．The moon and the sun together pull the sea．In some parts of the world，the difference between ‘high tide’（when the sea is very near to the land）and ‘low tide’ （when the sea is far away from the land）is very big．This is very important for ships． The moon is very different from the Earth．Gravity on the moon is six times weaker than that on the Earth．There isn't any air．DurinThis pair of sunglasses ____ very expensive. A. is B. are C. paysD. does