Telegraphic Plateau is a part of

1. A

   North Atlantic Ridge

   The Telegraph Plateau (Telegraphic Plateau) is a relatively flat segment of the Mid-Atlantic Ridge in the North Atlantic, historically associated with trans-Atlantic telegraph cables. That is why (a) is the official key.

2. B

   South Atlantic Ridge

   The South Atlantic Ridge is a different segment of the Mid-Atlantic Ridge south of the Equator; the named Telegraph Plateau is northern.

3. C

   Indian Ocean Ridge

   The Indian Ocean (Central Indian) Ridge is a separate spreading system; it does not host the Telegraph Plateau.

4. D

   None of these

   A correct parent ridge is named: North Atlantic. ‘None’ is wrong.

Summary. Official key is (a). The Telegraphic Plateau is part of the North Atlantic (Mid-Atlantic) Ridge, not the South Atlantic or Indian Ocean ridges.