Indigo cultivation in India declined by the beginning of the 20th century because of

1. A

   peasant resistance to the oppressive conduct of planters

   Peasant resistance. 1859–60 was earlier; decline by 1900 is the market.

2. B

   its unprofitability in the world market because of new inventions

   Unprofitable because of new inventions. Synthetic indigo (German, 1890s) crashed natural indigo.

3. C

   national leaders' opposition to the cultivation of indigo

   National leaders. Secondary to chemistry and prices.

4. D

   Government control over the planters

   Government control of planters. Not the keyed cause of the fade-out.

Summary. Official key is (b). Natural indigo lost the world market once synthetic indigo was invented and cheapened. Peasant revolt is the 1859 story, not the twentieth-century decline.