The correct answer is: B. 1-100 or steeper.
A material train is a type of train that is used to transport materials, such as coal, ore, and other bulk goods. Material trains are typically very long and heavy, and they can be difficult to control. For this reason, it is important to take special precautions when operating a material train, especially on gradients.
A gradient is a slope or incline. When a train is traveling up a gradient, it is working against gravity. This makes it more difficult for the train to move, and it can also cause the train to derail. For this reason, it is important to avoid detaching vehicles from a material train on a gradient.
If a vehicle is detached from a material train on a gradient, the train can become unbalanced and derail. This can be a very dangerous situation, and it can lead to serious injuries or death. For this reason, it is important to always follow the safety guidelines when operating a material train.
The other options are incorrect because they do not represent the correct gradient for a material train. Option A, ST 1-260, is the gradient for a passenger train. Option C, 1-400, is the gradient for a freight train. Option D, None of these, is incorrect because it does not represent any of the correct gradients.