children become expert at holding their breath under water e

children become expert at holding their breath under water even before they can walk.这句
话的翻译是：孩子们甚至在还没有学会走路时就已经能熟练地在水下屏住呼吸了,become在这里的用法.是不是过去不会,现在会了.就用become,换句话说就是过去从来没有的东西,现在有了,就用become.就和He became the proud owner of a bed shich had springs and a mattress这里把become翻译成生平第一次一样.