Writing is difficult because so many skills are involved. We must spell and form words correctly, and we must arrange sentences clearly. We must construct paragraphs logically, and we must pull paragraphs together so that they work to form a unified piece of writing. All these skills require frequent review, careful examination, and practice. The topic sentence of this paragraph is: ___. Writing is difficult because so many skills are involved We must spell and form words correctly, and we must arrange sentences clearly We must construct paragraphs logically, and we must pull paragraphs together so that they work to form a unified piece of writing All these skills require review, careful examination, and practice