Wire the thermometers up to trigger off an alarm bell if the temperature drops.把温度计用电线连上，这样温度下降后就会触发警铃。The drop in temperature condensed the steam to water.温度下降使蒸汽凝成了水。Dry soil cools rapidly when air temperatures fall.空气温度下降时，干燥的土壤很快冷却。The temperature fell after dark.天黑后温度下降了。