subsidy 什么时候用复数什么时候可以直接用单数什么时候必须用复数?

一般来说,
作为抽象、概念性名词用单数
作为具体、实际物体名词按语境可用单数或复数
例：
The company will provide a subsidy for overseas living allowance
Subsidies are provided to cover various additonal expenses
Tobacco subsidy is philosophically inconsistent with a country's healthcare strategy
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