<u><em>C) Write in complete sentences, don't use slang or filler words, and spell words correctly</em></u>
Explanation:
<u>Formal writing</u> is the one that is used in professional assignments that shows the academic skills of a person in conveying messages through f<u>ormal language</u> and writing techniques.
<u>Formal writing</u> avoids <u>colloquial vocabulary,</u> contractions, and grammatical mistakes and favors elevated language and elaborate descriptions.