在英语中，有许多短语形近异义，用法也截然不同，而有无定冠词the是它们的区别所在。因此，我们在日常的学习过程中要特别注意这些短语的区别，留心定冠词the。
1．at cost照成本价，照原价
I’ll sell all these goods to you at cost．我将按成本价把所有这些货卖给你。
at the cost of以……为代价，牺牲……
He saved the little boy at the cost of his own life．
他救了那个小男孩，却牺牲了自己的生命。
2．by day在白天
It is no use trying to escape by day．在白天逃跑是没有用的。
by the day按日计算
The employer paid the employee by the day．雇主按日付给雇工工资。
3．go to sea去当水手，出航
Owing to a strong wind，the ship could not go to sea．由于大风，船不能起航。
go to the sea去某一特定的海边
They usually go to the sea in midsummer．他们通常在仲夏到海滨去。
4．in care of由……转交
You may write to me in care of Miss Zhang．来信可由张小姐转交给我。
in the care of由……照看或处理
The library is in the care of Mrs James．图书馆由詹姆士太太负责
管理。
5．in case of万一
In case of fire，ring the alarm bell．万一失火，请按警铃。
in the case of至于……，就……来说
