The correct answer is option 'A', pulling gradient.

In hilly terrains, railway tracks face significant challenges due to the changes in elevation. To ensure safe and efficient train operation, a suitable gradient is provided. A gradient refers to the rate of change of vertical elevation with respect to the horizontal distance along the track. There are different types of gradients used in railway tracks, such as pulling gradient, momentum gradient, and helper gradient.

1. Pulling Gradient:
The pulling gradient is the most common type of gradient used in hilly terrains. It is designed to assist the locomotives in pulling the train uphill. In this type of gradient, the track is inclined upwards in the direction of train movement. This helps to overcome the gravitational forces acting against the train's motion. By providing a pulling gradient, the locomotives can exert the necessary pulling force to overcome the resistance and maintain a steady speed while ascending the hill.

2. Momentum Gradient:
The momentum gradient is another type of gradient used in railway tracks. It is designed to utilize the momentum gained by the train while descending a hill to aid in climbing the subsequent uphill section. In this type of gradient, the track is inclined downwards in the direction of train movement. As the train descends the hill, it gains kinetic energy, which can be utilized to overcome the resistance while ascending the next hill. The momentum gradient helps to reduce the strain on locomotives and save energy.

3. Helper Gradient:
The helper gradient is a special type of gradient used in steep or difficult sections of railway tracks. It involves the use of additional locomotives, known as helper engines, to assist the train in climbing uphill. The helper engines are attached to the train and provide additional pulling power to overcome the resistance. The helper engines are usually detached once the train reaches a relatively easier section of the track.

In conclusion, for a railway track in hilly terrain, the type of gradient provided is the pulling gradient. It helps the locomotives in overcoming the resistance and maintaining a steady speed while ascending the hill. The pulling gradient ensures safe and efficient train operation in challenging terrains.