sat 语法题!The codfish inhabits the shallow waters of the ocean

sat 语法题!
The codfish inhabits the shallow waters of the ocean; they are especially plentiful in {such areas as} the North American continental shelf,where the depth is rarely greater than 200 or 300 feet.
such areas as 但后面只有一个the North American continental shelf，为什么不用such area as？

在“such…as…”结构中,形容词 such 的词义是“诸如此类的,如此的,这类的”,后面的名词一般都用复数,因为是指那一类事物.而介词 as 的词义是“就像…”,其作用是引导同位语,表示举一个例子,所以后面的名词用单数即可.