Final answer:
Rocks become partially molten when the temperature exceeds their melting point, which can vary depending on the composition and pressure of the rocks. Additionally, the addition of water can also lower the melting temperature of rocks.
Step-by-step explanation:
The temperature at which rocks become partially molten depends on various factors, such as the composition and pressure of the rocks. In general, rocks start to melt when the temperature exceeds their melting point, which can range from a few hundred degrees Celsius to more than 1000 degrees Celsius. However, it's important to note that rocks can also become partially molten due to the addition of water, which lowers their melting temperature.