课文详注 Further notes on the text
1．…children become expert at holding their breath under water even before they can walk．……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。
（1）expert表示“熟练者”、“专家”，后面通常跟 at／in+ doing sth．结构（cf．第59课课文详注）：
Rex soon became an expert at opening the gate.
雷克斯很快成了开门的专家。
（2）hold one's breath 为固定短语，表示“屏住呼吸”：
When the film became very exciting, Tom and Sally
would hold their breath.
电影演到激动人心处时，汤姆和萨莉就会屏住呼吸。
Last night, when I heard a strange noise coming from the bar, I held my breath and listened carefully.
昨天晚上，当我听到酒吧间有奇怪的响声后便屏住呼吸仔细听。
2．It is not long before they are so accustomed to swimming that they can pick up weights from the floor of the pool. 他们很快便适应了游泳，以致能捡起池底的物品。
not long before 通常译为“不久”、“很快”。 so…that 引导的是结果状语从句。 pick up 表示“捡起”。weight 在这里指比重较大（因此能沉在水底）的物品。 be accustomed to 表示“习惯的”、“适应了的”，后面通常跟名词或动名词：
My mother is accustomed to getting up early.
我母亲习惯早起。
He soon became accustomed to his new job.
他很快适应了新工作。
3．A game that is very popular with these young swimmers is…这些幼小的游泳运动员非常喜爱的一种游戏是……
popular表示“受欢迎的”、“讨人喜欢的”，常与with或among连用：
Swimming is popular with these girls.
这些姑娘们喜爱游泳。
Mary is popular with / among children.
玛丽受孩子们的欢迎。
4．Tricycles are lined up on the floor of the pool…
三轮车并排放在游泳池底上……
line up 为短语动词，表示“（使）排成行／排队”：
Why are people lining up over there?
人们在那边排队干什么？
Line these chairs up, please.
请把这些椅子排好。
5．Whether they will ever become future Olympic champions, only time will tell. 他们将来是否能成为奥林匹克的冠军，这只能由时间来作出回答。
这是一个倒装句，宾语从句置于句首。通常，以疑问词引导的宾语从句会用于这种句型：
What made him do it, no one knows.
是什么使得他干了这事，没有人知道。
How they found out the truth, only George can tell.
他们是如何发现真相的，只有乔治能作出回答。