温かい___、スープを飲んでください。
Q. Which connective means 'while it's still (warm)'?
Translation
Please drink the soup while it's still warm.
Explanation
〜うちに means 'while a state lasts (before it changes)': 温かいうちに. ながら needs two actions by one subject, and ばかりに expresses a regretted cause.