The words that can be used for synonym is grotto...
grotto:
→ <span>a small picturesque cave, especially an artificial one in a park or garden
</span>→ <span>an indoor structure resembling a cave.
</span><span>
Opening is a synonym for cave, a cave is a grotto.</span>
B. But he stepped out briskly breathing deeply of the cold air
1. A
2. B
3. C
4. D
Hope this helped! btw they all went in order lol XD!