下層的英文：
substratum
參考例句：
Disadvantaged families
下層8kn-0.html" target="_blank" >貧困家庭
evergreen undershrub
常綠下層灌木
Party activists with lower middle class pedigrees are numerous.
黨內積極分子中中產階級下層出身的.很多。
The salt water, being more dense, flows upstream under the fresh water which is flowing downstream
淡水在上層向下流動，比重更大的鹽水在下層逆流向上。
At the nadir of...
在…的最下層[最低處]
He belongs to the lower middle class.
他來自中產階級下層。
The lower deck is more convenient.
下層甲板更方便些。
Tramps are in a low stratum of society.
流浪漢生活在社會的下層。
Tramps are from the lowest stratum of society
流浪漢來自社會最下層。
aristocrats who regarded the rabble with deep contempt.
對下層民眾極其蔑視的貴族們
substratum是什麼意思：
n. 下層;地基;根基
"For soft substratum, dig out the top layer (5 - 10 cm thick), sort out the animals, identify and count them."
若是軟基質,用小鏟挖出表面5-10釐米厚的基質,找出砂泥中的動物,點算和鑑定。
