Final answer:
To preserve the taste of Rachel's lemonade, the correct ratio of lemon juice to sugar water should remain at 1:5, which is answer choice D.
Step-by-step explanation:
Rachel was making lemonade, and she used a ratio of 1 cup of lemon juice to 5 cups of sugar water. To achieve lemonade that tastes the same, the ratio of lemon juice to sugar water must remain constant. The correct answer is D) 1:5, meaning for every cup of lemon juice, five cups of sugar water are needed to preserve the flavour profile of the lemonade.