熱があるなら、早く寝た___いいですよ。
Q. Which completes the advice 'you'd better go to bed early'?
Translation
If you have a fever, you'd better go to bed early.
Explanation
Advice uses plain past + ほうがいい: 寝たほうがいい. The past form is idiomatic even though the action is future. ことがいい and ものがいい are not set patterns.