Hello, I find myself stuck on this question, i am uncertain on what type of market structure it resembles

Coles and Woolworths dominate the Australian grocery retail (AGR hereafter) sector. Which type of market structure does this sector resemble? explain the likely reasons for the prevalence of this type of market structure in the AGR sector.

Is the dominance of Coles and Woolworths in the AGR sector strength or a weakness for the Australian economy? Explain using relevant examples.