An idiom/phrase is given in bold. Following this idiom/phrase are given three sentences, which use the given idiom/phrase. The idiom/phrase may or may not be used correctly in one or more sentences. Identify the sentence(s) that use(s) the idioms/phrases incorrectly either in grammar or context and mark the answer accordingly.
Let the cat out of the bag
I. He let the cat out of the bag when he accidentally mentioned the surprise party.
II. The magician let the cat out of the bag during his performance, shocking the audience.
III. She let the cat out of the bag by telling her friend about the job promotion before it was officially announced.
Which sentence(s) use(s) the idiom incorrectly?