The shelf should be six feet above thelevelofthefloor.
架子会放在高出地板六英尺的地方。
2
Levelofthefloor gradually follows the gently sloping terrain.
地板的水平高度随倾斜的地形而变化。
3
Caveat: the researchers couldn't account for the presence of noise barriers or thefloorlevel on which the subjects lived, factors that would influence traffic-noise exposure.