I recommend that Rachel use simple and compound sentences to effectively communicate her message to her younger brother in fourth grade.
Simple sentences are clear and easy to understand, which is important when giving instructions to a younger child. For example, Rachel could say "Put your clothes in the laundry basket" as a simple sentence that is straight to the point and easy to follow.
Compound sentences can also be effective in providing more detailed instructions or multiple steps in one sentence. For example, Rachel could say "Sort your clothes by color, then put them in the washing machine" as a compound sentence that breaks down the task into two separate actions.
By using a combination of simple and compound sentences, Rachel can provide clear and concise instructions that her younger brother can easily follow and refer to later.