Final answer:
The change in viscosity of a melt is directly proportional to the change in temperature and the silica content. Therefore, the correct option is B,D.
Step-by-step explanation:
The change in viscosity of a melt is directly proportional to the change in temperature and the silica content.
When the temperature of a melt increases, the molecules move more rapidly, which enables them to overcome the intermolecular forces that hold them together. This results in a decrease in viscosity.
Similarly, an increase in the silica content of a melt leads to a higher viscosity due to stronger intermolecular forces between the silica molecules.