What Is a "Course of Dealing" for the Purpose of Incorporating

Multiple Choice

What is a "course of dealing" for the purpose of incorporating terms?

A) A buys widgets from B once a year for five years
B) A buys widgets from B every couple of months, each time after negotiating the terms.
C) A buys widgets from B every couple of months, on B's standard terms.
D) A has bought widgets from B once before.