Q: In medieval India, the process of indigo extraction underwent great improvement as a result of the:
(a)use of fertilizer enhancing the quality of indigo crop.
(b)introduction of mechanical crushing tools for indigo stems.
(c)use of gypsum and lime mortars in making the inner surfaces of indigo vats water-proof.
(d)employment of slave labour in quick desilting of indigo crucibles.
Correct Answer: (c)