Addition, subtraction, multiplication, and division are binary operations.

加、减、乘、除都是二元运算。

The difference is found by subtraction.

用减法得出差。

Objective:To illustrate the value of digital subtraction dacryocystography in the diagnosis of lacrimal duct obstruction.

数字减影泪道造影术在临床检查泪道阻塞中的应用值。