The correct answer is: C. more than
The insulation level of the line is the maximum voltage that the line can withstand without breaking down. The insulation level of the station equipment is the maximum voltage that the equipment can withstand without breaking down. The insulation level of the line must be greater than the insulation level of the station equipment to ensure that the line does not break down when it is connected to the station equipment.
Option A: less than is incorrect because the insulation level of the line must be greater than the insulation level of the station equipment.
Option B: same as is incorrect because the insulation level of the line must be greater than the insulation level of the station equipment.
Option D: proportional to is incorrect because the insulation level of the line is not proportional to the insulation level of the station equipment. The insulation level of the line must be greater than the insulation level of the station equipment, but it does not have to be a specific multiple of the insulation level of the station equipment.
Option E: not directly related with is incorrect because the insulation level of the line is directly related to the insulation level of the station equipment. The insulation level of the line must be greater than the insulation level of the station equipment to ensure that the line does not break down when it is connected to the station equipment.