The sea is the biggest unknown part of our world. It covers about seventy-one per cent of the Earth. There is still much to be discovered about the huge water. If the ocean water could be removed, the sea floor with  (it) wide valleys and irregular (不规则的) mountains would be an unbelievable sight.

    Tourists can explore the world under the waves without  (get) wet nowadays. From tourist submarines (潜艇)  underwater meals, undersea travelling is more and more popular.

    Travelling by submarine  (grow) fast in the past ten years. Now, tourists can visit many beautiful places which are famous for their water, including the water around Okinawa and Taiwan's Green Island. The submarines carry nearly two million  (tourist) each year. Large windows offer passengers wonderful views when the submarines explore  (colour) animals and plants under the water. Most one-hour tours cost about $80.

    If tourists want to have  unforgettable experience, they can enjoy fine food under the sea. Several years ago, the Hilton Maldives Resort  (open) the world's first underwater restaurant, Ithaa. Tourists walk downstairs into the restaurant, which lies 35 feet under the waves of the Indian Ocean. The walls of the restaurant  (make) of strong glass, and tourists can enjoy a panoramic (全景的) ocean view. This excellent view doesn't come cheap  it costs about 1,300 yuan per person! Be sure to book a seat early too. There are only 14 seats for tourists in the restaurant.