add subtract

• 加减

add subtract的用法和样例：

例句

1. Children should be able to add and substract in the third grade.
   儿童应该在三年级的时候能够进行加减运算。
2. The idea that a machine could be built to add and subtract was an early step.
   制造一种能进行加减运算的机器的设想是历史的第一步。