a. 楼下的

[ adj ]
on or of lower floors of a building
<adj.all>
the downstairs (or downstair) phone

downstair \downstair\, downstairs \downstairs\adj.
on or of the lower floors of a building, especially the
ground floor; as, the downstairs (or downstair phone; the
house has no downstairs bathroom. Opposite of {upstairs}.
[WordNet 1.5]