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

加、、乘、除都是二元运算。

The difference is found by subtraction.

用法得出差额。

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

评价影泪道造影术在临床检查泪道阻塞中的应用价值。