Choose the option that best completes the sentence using an appropriate…

Concept: when a blank must be filled with an adjective, the sense of that adjective is fixed by the rest of the sentence, not by grammar alone. A result clause attached to the noun ("a/an ______ ending that made everyone smile") is the semantic clue: the adjective has to name the quality that could produce that stated result.

Application: the result stated here is that the ending "made everyone smile", i.e. it produced happiness in every viewer. The blank therefore needs an adjective whose meaning is "full of happiness". "Joyful" means filled with or expressing great joy, so a joyful ending is an ending whose events are happy — precisely an ending that would leave a whole audience smiling. The completed sentence reads: The movie had a joyful ending that made everyone smile.

Contrast: word class does not separate these four — each of them is an adjective that can describe an ending — and the frame is written "a/an", so the article gives nothing away either; the decision rests purely on meaning.

• "Painful" means causing pain or distress, so a painful ending would upset viewers rather than make them smile — the opposite emotional direction.

• "Ironical" (a form of "ironic") means marked by irony: the outcome contradicts what was expected. Irony describes a twist in expectation and carries no sense of happiness, so an ironical ending may just as easily be bitter.

• "Thoughtful" means absorbed in serious thought, or considerate towards others. It names reflection or kindness, not shared happiness, so a thoughtful ending would leave viewers thinking rather than smiling.

Cross-check: use the substitution test — put each adjective in the blank and ask whether "that made everyone smile" still follows as a natural consequence. It follows for "joyful", whose meaning is itself happiness; it does not follow for a painful, ironical or thoughtful ending, none of which entails a smile.