(a), (b) and (c) are the correct answers. Ploughing, harrowing, and inter-culturing are the broad groups of tillage operations. Tillage: It is the mechanical manipulation of soil with tools and implements for obtaining conditions ideal for seed germination, seedling establishment, and growth of the crop. Objectives of tillage:To create conditions in the soil suited for better growth of crops. To control weeds effectively. To make the soil capable of absorbing more rainwater. To mix up manure and fertilizers effectively in the soil. Providing adequate seed-soil contact permit water flow to seed and seedling roots. Primary tillage:The operations are performed to open up any cultivable land to prepare a seedbed for growing crops known as primary tillage. Animal-drawn implements in primary tillage mostly include MB-plough. Tractor-drawn implements include MB-plough, disc plough, subsoil plough, chisel plough, and other similar implements. Secondary tillageLighter or finer operations performed on the soil after primary tillage is known as secondary tillage. Harrowing is to be done to a shallow depth to crush the clods and to uproot the remaining weeds and stubbles. Seedbed preparation and intercultural operations are done up to a depth of 15 cm. Secondary tillage implements: Disc harrow, spike tooth harrow, spring tooth harrow, acme harrow, etc.