问题描述：
助动词和情态动词改错问题1
They should (use) coal,but they had to use oil instead,because there remained little coal.
括号里的是错的.为什么说should have used,而不说could use呢?
说should have used的话是说“应该用了”,说could use的话是说“原可用”,请问有啥米区别吗?
They should (use) coal,but they had to use oil instead,because there remained little coal.
括号里的是错的.为什么说should have used,而不说could use呢?
说should have used的话是说“应该用了”,说could use的话是说“原可用”,请问有啥米区别吗?
问题解答：
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