Read the reading below carefully, and then complete it with the best option A, B, C or D given below:
These features were discovered and explored (1) ______ in the late 1940s. The Lomonosov Ridge, the major Ridge, cuts the Arctic Basin (2) ______ in half, extending as a submarine bridge 1,800 km (1,100 mi) (3) ______ Siberia to the northwestern tip of Greenland. Parallel (4) ______ it are two shorter Ridges: the Alpha Ridge on the North American (5) ______ , defining the Canada and Makarov basins, (6) ______ the Arctic Mid-Ocean Ridge on the Eurasian side, (7) ______ the Nansen and Amundsen basins. The average (8) ______ of the Arctic Ocean is only 1,300 m (4,300 ft) (9) ______ the vast shallow expanses on the continental shelves. The deepest (10) ______ in the Arctic Ocean is 5,450 m (17,880 ft).

These features were discovered and explored (1) ______ in the late 1940s.