20.According to the passage, which of the following statements is true? (A) Large cruise liners run by global companies are now forbidden to enter the Antarctic areas. (B) Scientists have proven that there has been no impact from several decades of Antarctic tourism. (C) By the end of 2010, the number of tourists will be sixteen times of that in the early 90s. (D) The fact that tourists have been on the increase does not worry environmentalists.