Steel slag can be used for several purposes, and all of the options listed are valid applications. Statement 1 is correct. Steel slag is a common and cost-effective material for use in road base construction due to its high durability, strength, and drainage properties. Statement 2 is correct. Crushed steel slag can be used as an amendment for agricultural soil. It can improve drainage, provide some essential nutrients, and even help suppress weeds. Statement 3 is correct. Steel slag can be partially substituted for some raw materials in cement production, reducing the need for quarrying and lowering the environmental impact of cement manufacturing. Therefore, the correct answer is 1, 2, and 3.