Option a is the correct answer
When the temperature of the rock rises above the melting point of minerals present in the rock results in melting of rock.
Rock contains different types of minerals having different melting points. Thus, not all the parts of rock melts at same time. Some of the minerals melt at high temperatures whereas some of the minerals melt at low temperatures. Hence, decrease in melting temperature and increase in melting temperatures due to water depends upon the composition of rock.