Select the most suitable option to substitute the highlighted part in the sentence.
I gave my best dress to her on condition that she return it the very next day in a clean condition.

Correct option is C

Explanation:
This is a subjunctive clause (expressing demand, suggestion, condition) after “on the condition that…”.
In subjunctive mood, the base form of the verb (“return”) is used even if the subject is third person.
(a) would return – Future-in-the-past; not required in this structure.
(b) had return – Grammatically incorrect; past perfect is “had returned”.
(d) returned – Simple past; doesn’t express the hypothetical or suggested action.
Grammar Rule:
Use base verb after expressions like “on condition that”, “suggest that”, “demand that”.
Example: He insisted that she be present.