Which CSS3 property should you use?

You are developing a web page that will be divided into three vertical sections. The main content of the site will be placed in the center section.
The two outer sections will contain advertisements.
You have the following requirements:
The main content section must be set to two timesthe width of the advertising sections.
The layout must be specified by using the CSS3 flexible box model.
You need to ensure that the visual layout of the page meets the requirements.
Which CSS3 property should you use?

A.
box-orient

B.
box-flex-group

C.
box-flex

D.
box-direction