45
90
145
150
Answer is Right!
Answer is Wrong!
The correct answer is: B. 90
The first flag man to the approaching train must start at not less than 90 meters from the last detonator. This is to ensure that there is enough space for the train to stop safely in the event of an emergency.
Option A: 45 meters is too close. If the train were to stop suddenly, the flag man would be in danger of being hit.
Option C: 145 meters is too far. If the train were to stop suddenly, the flag man would not be able to reach the detonator in time to warn the train.
Option D: 150 meters is also too far. The same reasoning applies as for option C.
Therefore, the correct answer is B. 90 meters.