Which substances are used to lower the temperature required to liquefy asphalt?

The correct choice, which refers to cutbacks and emulsions, is significant because these substances are specifically designed to modify the properties of asphalt, making it easier to handle and application-friendly.

Cutbacks are produced by blending asphalt with a solvent, typically a petroleum product. This reduces the viscosity of the asphalt, allowing it to be applied at lower temperatures which can be crucial for certain conditions such as colder weather or when working with materials that are sensitive to heat.

Emulsions, on the other hand, consist of tiny droplets of asphalt dispersed in water with the aid of surfactants. They enable the use of asphalt in a liquid state at lower temperatures without the need for significant heating, thus making them an efficient choice for paving and sealing applications. Moreover, emulsions help in reducing fumes during application and are eco-friendlier due to the lower energy requirement.

Other choices focus on different aspects of materials used in asphalt applications but do not directly target the specific need to lower the temperature for liquefying asphalt, which is critical for efficient application and performance. Hence, their absence from consideration in this scenario.