Explanation:

- The main reason behind Champaran Satyagraha was the forced cultivation of indigo by peasants under the oppressive Tinkathia system.

- Tinkathia System: Peasants were forced to grow indigo on 3/20th (about 15%) of their land for European planters, often at very low prices.

- Sharahbeshi: This referred to a revenue system, not directly related to the Champaran issue.

- Tawan: It was a system where a lump sum fine was charged from peasants, not the central issue in Champaran.

- Baghidari: This land tenure system meant sharing produce between landlord and tenant, but was not key in Champaran.

- Correct Answer: Option 1 – Tinkathia.