简可以一下子把准确的数量告诉你。
Jane can tell you the correct amount off the top of her head.
当然，那个数字只是估计，没人确切知道准确的数量。
That figure, of course, is just an estimate-nobody really knows exactly how many.
可是你牺牲了灵活性，你必须去知道准确的数量，生命周期和对象类型当你在写程序的时候。
However, you sacrifice flexibility because you must know the exact quantity, lifetime and type of objects while you're writing the program.
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