Concept:Tillage implements are grouped into primary and secondary types based on the stage of land preparation they perform.
Explanation:Primary tillage implements, such as the plough and disc plough, are used to break and turn the soil for the first time.
Secondary tillage implements are used after primary tillage to refine the seedbed.
The harrow is a secondary tillage implement that breaks up soil clods, levels the land, and prepares a smooth seedbed.
It is typically used immediately after ploughing and before ridging.
A ridger is mainly used for making ridges, not for secondary tillage.
Answer:A. Harrow