The correct answer is: A. 48 hours.
A line block is a temporary closure of a railway line. It is used for a variety of purposes, such as maintenance, construction, and emergency repairs. To apply for a line block, the notice shall be given to DRM not less than 48 hours in advance. This is to allow the DRM to arrange for the necessary personnel and equipment to be on site at the time of the line block.
Option B is incorrect because it is not the minimum notice period required. Option C is incorrect because it is less than the minimum notice period required. Option D is incorrect because it is not one of the options provided.