Final answer:
Word is the most effective Office Online app for writing letters. It provides a wide range of formatting options and templates that help users create professional-looking letters easily.
Step-by-step explanation:
Word is the most effective Office Online app for writing letters. It provides a wide range of formatting options and templates that help users create professional-looking letters easily. With features like spell check, grammar check, and the ability to add images and diagrams, Word is a versatile app for writing various types of documents.
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