“Iron out” means to

The phrasal verb "iron out" means to resolve or finalize minor details often issues in plans or processes making "complete small details" correct. "Make problems" is the opposite "plan ahead" is unrelated and "none of these" is incorrect. This phrase is common in project management or negotiations where smoothing out issues is key. Mastering such phrasal verbs improves fluency in English particularly in professional or academic settings. Precise language ensures clear communication and effective problem-solving in contexts requiring attention to detail or resolution.