Answer:
Addition of acid.
Decrease in temperature.
Step-by-step explanation:
Calcium carbon is sparingly soluble in water at room temperature.
If we wish to increase its solubility in water, we can decrease the temperature as it is unusual property of calcium carbonate that its solubility increases with the decrease in temperature.
The solubility can also be increased by addition of acid (or dissolution of carbon dioxide which will produced carbonic acid). The presence of acid converts the calcium carbonate to calcium bicarbonate which is soluble in water.