Final answer:
The viscosity of magma or lava is primarily controlled by its composition and temperature, hence the correct answer is D. A & B. Factors like the amount of silica in the magma and the heat levels are critical in determining how fluid the magma or lava will be.
Step-by-step explanation:
The viscosity of a magma or lava is often controlled by B. composition and A. temperature of the magma or lava. Therefore, the correct answer is D. A & B. The viscosity, which is the resistance of a fluid to flow, can be influenced by several factors. The chemical composition plays a significant role because different elements and compounds can affect the melting point and the behavior of the molten material. Silica-rich magmas, for example, tend to be more viscous than magmas with lower silica content.
Furthermore, the temperature of the magma or lava is critical in determining its viscosity. Higher temperatures generally reduce the viscosity, allowing the magma or lava to flow more easily. When lava cools down, its viscosity increases, making it more resistant to flow. Conditions such as the amount of vent space or the pressure of the magma are not typically direct factors affecting viscosity, but rather influence the eruption style and the possibility of an eruption occurring.