Religion established a rigid caste system, but it was formally abolished in the mid-20th century? islam jainism hinduism shinto

Hinduism is the correct answer.

Explanation:

The caste system was found in Hinduism. It divided society into four sections. In the beginning there were only four castes and it was known as Varna system. Portuguese were the first one to label it as caste system. Priests, warriors, traders and farmers , and at the bottom were labourers and service providers. It wasn't really a part of Hinduism at first but it did began at the same time as Hinduism and remained in Indian for thousands of years even when the Aryan leaders were replace. It was abolished in 1950 when Indian became a democratic republic.  

Note: One should be careful while reading about the Aryans. The theory that states that Aryans invaded India in ancient times is still contested being argued by the scholars and historians are divided over it.

your answer will most likely be a.