The best response that follows the R.A.C.E strategy for responding to the prompt "In 1-2 sentences, explain how a dictionary helps readers better understand familiar words." is:
"A dictionary helps readers better understand familiar words by providing a definition, part of speech, pronunciation, etc. These things help readers to best determine the meaning and relevance of a word."
This response restates the prompt by explaining how a dictionary helps readers, answers the prompt by stating that a dictionary provides definition, part of speech, pronunciation, etc., cites evidence by listing examples of the information provided by a dictionary, and explains the evidence by stating how these things help readers determine the meaning and relevance of a word.