tier
n
any of a series of rows (esp of seats) or parts of a structure placed one above the other 一排(尤指座位); (阶梯式的)一层
a box in the first tier, ie in atheatre (剧院中的)第一排的一个包厢
a wedding-cakewith three tiers/a three-tier wedding-cake 有三层的结婚蛋糕. =>illus at layer 见 layer 插图.
Snakes did not acquire their poison for use against man but for use against prey such as rats and mice, and the effects on these of viperine poison is almost immediate.