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1·He's bought a big TV at vast expense so that everyone can see properly.

他花了很多钱买了台大电视，这样人人都可以看清楚了。《柯林斯英汉双解大词典》

2·He has bought a specially big TV at vast expense so that everyone can see it properly.

他花了很多钱买了一个特别的电视，为了能让大家都看清楚。

3·Moving and equipping the house has been a vast expense and, after splitting our savings, X and I haven't talked about money at all.

搬家和买家具是一笔很大的费用，而在我们的储蓄分开后，X和我根本就没有谈过钱这方面的事情。