a spiral staircase的用法和样例：
- So the giant shoved it open with his shoulder. There was a spiral staircase.
- The two strands of the double helix are linked by pairs of nucleic acids like the treads in a spiral staircase.
- It was reached by a spiral staircase which terminated in the corner of the room at a square hole like the hatchway of a ship.
- It has a double helix structure, like a spiral staircase, which was discovered by Francis Crick and James Watson in the Cavendish lab at Cambridge in 1953.
- Imagine walking up a spiral staircase with your left hand on the inner banister and your right hand on the outer one.Such a staircase is a right-handed helix.
- a spiral staircase(= a set of stairs that curve upwards around a central post)