What relation is a door to a doorstep?

谜面是：门和门阶的关系是什么？
谜底：only one step away
only one step away

The doorstep is a way that leads to the door.

差一步（STEP）一语双关

问：What relation is a door to a doorstep?
门和台阶之间是什么关系？
答：only one step away
只差一步
OK?!

门和台阶之间是什么关系？ 差一步