Question

two months their

英语提问：以下复合句中when后面为何只有two months old.这是怎么回事,
At a swimming pool in Los Angeles,children who are taught to hold their breath under water before they can walk often begin learning to swim when two months old.

Answer 1

在洛杉矶的游泳池里,学走路之前会先学在水里憋气的孩子们通常在两个月大就开始学游泳.
这个句子较复杂的是后半句.句子主干是chileren begin learning to swim.who are taught to hold their breath under water before they can walk这是个定语从句,来修饰先行词children,表示学走路前先学会在水里憋气的孩子们.后面的when two months old 是时间状语从句,完整形式是when children are two months old,因为这个从句的主语和主句的主语一致,都是children,系动词可以省掉,所以就简化为when two months old.