The best synonym for "treacherous" in the context of the sentence provided is "dangerous." Here's why:
1. **Tremendous** does not mean the same as treacherous. "Tremendous" means very large or great, whereas "treacherous" means hazardous or risky.
2. **Smooth** is the opposite of treacherous. Something smooth is generally easy to traverse, unlike something treacherous, which is full of risks and dangers.
3. **Dangerous** is the most appropriate synonym for treacherous in this context. Treacherous describes something that is full of hazards, risks, or potential harm, which aligns with the description of the mountain passage in the sentence.
4. **Straight** means extending or moving uniformly in one direction, without curves or angles. It does not convey the same meaning as treacherous, which implies danger and unpredictability.
Therefore, the best synonym for treacherous in the sentence "The steep mountain passage was narrow and treacherous" is "dangerous," as it captures the idea of a hazardous and risky environment.
