The correct answer is A. 1 meter.
The depth of exploration for each storey (or story) of a building should be 1 meter. This is because the average height of a person is 1.7 meters, and the average depth of a human body is 0.6 meters. Therefore, if the depth of exploration is less than 1 meter, there is a risk that the person may not be able to stand up straight or move around freely. If the depth of exploration is more than 1 meter, there is a risk that the person may become trapped or suffocate.
Option B is incorrect because it is not deep enough to allow a person to stand up straight or move around freely. Option C is incorrect because it is too deep and there is a risk that the person may become trapped or suffocate. Option D is incorrect because it is not a valid option.