ANS:A - large suspended organic solids

Primary treatment of sewage primarily consists of the removal of large suspended organic solids. During primary treatment, sewage passes through processes like screening and sedimentation, where large debris, such as sticks, rags, and other solid materials, are removed from the wastewater. This helps to protect downstream processes and equipment in sewage treatment plants from damage and clogging. While primary treatment may also remove some oil and grease, sand and grit, and floating materials, its primary focus is on the removal of large suspended organic solids. Therefore, this is the most accurate option among those provided.