The correct answer is option 4, "4 only."

Option 1, which states that private retail trading was strictly forbidden, is incorrect. Under Lenin`s New Economic Policy (NEP), private retail trading was allowed and even encouraged in order to stimulate economic activity and meet consumer demand.

Option 2, which states that private enterprise was strictly forbidden, is incorrect. The NEP allowed for small-scale private enterprise, particularly in agriculture and small industries. This was seen as a temporary measure to revive the Soviet economy after the devastation of the Russian Civil War.

Option 3, which states that peasants were not allowed to sell their surplus, is incorrect. The NEP actually allowed peasants to sell their surplus agricultural products in the open market instead of being subject to strict state control. This provided incentives for increased agricultural production and helped alleviate food shortages.

Option 4, which states that concessions were allowed to foreign capitalists and the state retained the option of purchasing their products, is indeed a feature of Lenin`s NEP. This was done to attract foreign investment and expertise, particularly in the larger industrial sectors of the economy. The state retained control and had the option to purchase the products of these foreign-owned enterprises.

Overall, the correct feature of Lenin`s NEP