Read the reading below carefully, and then complete it with the best option A, B, C or D given below:
Approximately one-third of the Arctic (1) _______ is underlain by continental shelf, (2) _______ includes a broad shelf north of Eurasia and the narrower shelves of North America and Greenland. Seaward of the continental shelves (3) _______ the Arctic Basin proper, which is subdivided (4) _______ a set of three parallel ridges and four basins (also (5) _______ as deeps).

Approximately one-third of the Arctic (1) _______ is underlain by continental shelf, .......