The grain tax is implemented, and the surplus grain after farmers pay taxes can be bought and sold freely in the market; Return some nationalized enterprises and allow domestic and foreign capital economy to operate; Conduct free trade within a certain range, allow commodity production, and restore commodity currency relations. -This is written in the book.

I think, D is Stalin's; B no, there was no landlord class in Russia at that time; A it's not right either, because surplus grain is not allowed to be collected. The collection of surplus grain is "wartime communism". The new economic policy means that farmers' surplus grain after tax payment can be bought and sold freely in the market. So c is right.