D.
In order to make sure your essay is coherent and the reader can follow it easily, you want to make sure that you've started with proper planning and outlining. If you have a clear thought on what order the main ideas will appear in, you can make sure they make sense in that order. Additionally, if you repeat important words, phrases, and ideas throughout the paper the reader will be reminded of what's most important which will help make it clearer and easier to understand and follow.
