The primary duty of our countrymen at present should be to curb such social evils as casteism and untouchability.

Answer: Option C

Curb : a check or restraint on something.
Recommend : put forward (someone or something) with approval as being suitable for a particular purpose or role.
Restore : bring back or re-establish (a previous right, practice, or situation).
Encourage : give support, confidence, or hope to (someone).
Reinstate : restore (someone or something) to their former position or state.

Antonym of Curb is Encourage